diff --git a/lldb/include/lldb/Interpreter/CommandObject.h b/lldb/include/lldb/Interpreter/CommandObject.h
index 54ee5ac26623..fb6ab91433f6 100644
--- a/lldb/include/lldb/Interpreter/CommandObject.h
+++ b/lldb/include/lldb/Interpreter/CommandObject.h
@@ -481,6 +481,12 @@ protected:
     // is present you want to prime the dummy target with entities that will be copied over to new targets.
     Target *GetSelectedOrDummyTarget(bool prefer_dummy = false);
     Target *GetDummyTarget();
+    
+    // If a command needs to use the "current" thread, use this call.
+    // Command objects will have an ExecutionContext to use, and that may or may not have a thread in it.  If it
+    // does, you should use that by default, if not, then use the ExecutionContext's target's selected thread, etc...
+    // This call insulates you from the details of this calculation.
+    Thread *GetDefaultThread();
 
     //------------------------------------------------------------------
     /// Check the command to make sure anything required by this
diff --git a/lldb/include/lldb/Target/ThreadList.h b/lldb/include/lldb/Target/ThreadList.h
index e6489b25e558..c5dbb199ad7d 100644
--- a/lldb/include/lldb/Target/ThreadList.h
+++ b/lldb/include/lldb/Target/ThreadList.h
@@ -16,6 +16,7 @@
 #include "lldb/Core/UserID.h"
 #include "lldb/Utility/Iterable.h"
 #include "lldb/Target/ThreadCollection.h"
+#include "lldb/Target/Thread.h"
 
 namespace lldb_private {
 
@@ -44,7 +45,43 @@ public:
     // selected at index 0.
     lldb::ThreadSP
     GetSelectedThread ();
+    
+    // Manage the thread to use for running expressions.  This is usually the Selected thread,
+    // but sometimes (e.g. when evaluating breakpoint conditions & stop hooks) it isn't.
+    class ExpressionExecutionThreadPusher
+    {
+        public:
+        ExpressionExecutionThreadPusher(ThreadList &thread_list, lldb::tid_t tid) :
+            m_thread_list(&thread_list),
+            m_tid(tid)
+        {
+            m_thread_list->PushExpressionExecutionThread(m_tid);
+        }
+        
+        ExpressionExecutionThreadPusher(lldb::ThreadSP thread_sp);
+        
+        ~ExpressionExecutionThreadPusher()
+        {
+            if (m_thread_list)
+                m_thread_list->PopExpressionExecutionThread(m_tid);
+        }
+        
+        private:
+            ThreadList *m_thread_list;
+            lldb::tid_t m_tid;
+    };
 
+    lldb::ThreadSP
+    GetExpressionExecutionThread();
+    
+protected:
+    void
+    PushExpressionExecutionThread(lldb::tid_t tid);
+    
+    void
+    PopExpressionExecutionThread(lldb::tid_t tid);
+
+public:
     bool
     SetSelectedThreadByID (lldb::tid_t tid, bool notify = false);
 
@@ -147,6 +184,7 @@ protected:
     Process *m_process; ///< The process that manages this thread list.
     uint32_t m_stop_id; ///< The process stop ID that this thread list is valid for.
     lldb::tid_t m_selected_tid;  ///< For targets that need the notion of a current thread.
+    std::vector<lldb::tid_t> m_expression_tid_stack;
 
 private:
 
diff --git a/lldb/source/Commands/CommandObjectProcess.cpp b/lldb/source/Commands/CommandObjectProcess.cpp
index cef99b759dd6..857440b7af78 100644
--- a/lldb/source/Commands/CommandObjectProcess.cpp
+++ b/lldb/source/Commands/CommandObjectProcess.cpp
@@ -708,7 +708,7 @@ protected:
 
             if (m_options.m_ignore > 0)
             {
-                ThreadSP sel_thread_sp(process->GetThreadList().GetSelectedThread());
+                ThreadSP sel_thread_sp(GetDefaultThread()->shared_from_this());
                 if (sel_thread_sp)
                 {
                     StopInfoSP stop_info_sp = sel_thread_sp->GetStopInfo();
diff --git a/lldb/source/Commands/CommandObjectThread.cpp b/lldb/source/Commands/CommandObjectThread.cpp
index fa273d6b7d96..988eb5026a8f 100644
--- a/lldb/source/Commands/CommandObjectThread.cpp
+++ b/lldb/source/Commands/CommandObjectThread.cpp
@@ -509,7 +509,8 @@ protected:
 
         if (command.GetArgumentCount() == 0)
         {
-            thread = process->GetThreadList().GetSelectedThread().get();
+            thread = GetDefaultThread();
+
             if (thread == nullptr)
             {
                 result.AppendError ("no selected thread in process");
@@ -919,7 +920,7 @@ public:
                 // lock before calling process->Resume below.
                 Mutex::Locker locker (process->GetThreadList().GetMutex());
                 const uint32_t num_threads = process->GetThreadList().GetSize();
-                Thread *current_thread = process->GetThreadList().GetSelectedThread().get();
+                Thread *current_thread = GetDefaultThread();
                 if (current_thread == nullptr)
                 {
                     result.AppendError ("the process doesn't have a current thread");
@@ -1170,7 +1171,7 @@ protected:
 
             if (m_options.m_thread_idx == LLDB_INVALID_THREAD_ID)
             {
-                thread = process->GetThreadList().GetSelectedThread().get();
+                thread = GetDefaultThread();
             }
             else
             {
diff --git a/lldb/source/Commands/CommandObjectType.cpp b/lldb/source/Commands/CommandObjectType.cpp
index acbcdbb69eff..971506bd9e0c 100644
--- a/lldb/source/Commands/CommandObjectType.cpp
+++ b/lldb/source/Commands/CommandObjectType.cpp
@@ -3423,8 +3423,16 @@ protected:
     bool
     DoExecute (const char *command, CommandReturnObject &result) override
     {
-        auto target_sp = m_interpreter.GetDebugger().GetSelectedTarget();
-        auto frame_sp = target_sp->GetProcessSP()->GetThreadList().GetSelectedThread()->GetSelectedFrame();
+        TargetSP target_sp = m_interpreter.GetDebugger().GetSelectedTarget();
+        Thread *thread = GetDefaultThread();
+        if (!thread)
+        {
+            result.AppendError("no default thread");
+            result.SetStatus(lldb::eReturnStatusFailed);
+            return false;
+        }
+        
+        StackFrameSP frame_sp = thread->GetSelectedFrame();
         ValueObjectSP result_valobj_sp;
         EvaluateExpressionOptions options;
         lldb::ExpressionResults expr_result = target_sp->EvaluateExpression(command, frame_sp.get(), result_valobj_sp, options);
diff --git a/lldb/source/DataFormatters/FormattersHelpers.cpp b/lldb/source/DataFormatters/FormattersHelpers.cpp
index 4b0e82e975e4..6c1b8c37480b 100644
--- a/lldb/source/DataFormatters/FormattersHelpers.cpp
+++ b/lldb/source/DataFormatters/FormattersHelpers.cpp
@@ -140,13 +140,18 @@ lldb_private::formatters::GetViableFrame (ExecutionContext exe_ctx)
     if (frame)
         return frame;
     
+    Thread *thread = exe_ctx.GetThreadPtr();
+    if (thread)
+        return thread->GetSelectedFrame().get();
+
     Process* process = exe_ctx.GetProcessPtr();
     if (!process)
         return nullptr;
     
-    ThreadSP thread_sp(process->GetThreadList().GetSelectedThread());
-    if (thread_sp)
-        return thread_sp->GetSelectedFrame().get();
+    thread = process->GetThreadList().GetSelectedThread().get();
+    if (thread)
+        return thread->GetSelectedFrame().get();
+    
     return nullptr;
 }
 
diff --git a/lldb/source/Interpreter/CommandObject.cpp b/lldb/source/Interpreter/CommandObject.cpp
index 07941ea1cc24..0993cd33a5a9 100644
--- a/lldb/source/Interpreter/CommandObject.cpp
+++ b/lldb/source/Interpreter/CommandObject.cpp
@@ -1027,6 +1027,31 @@ CommandObject::GetSelectedOrDummyTarget(bool prefer_dummy)
     return m_interpreter.GetDebugger().GetSelectedOrDummyTarget(prefer_dummy);
 }
 
+Thread *
+CommandObject::GetDefaultThread()
+{
+    Thread *thread_to_use = m_exe_ctx.GetThreadPtr();
+    if (thread_to_use)
+        return thread_to_use;
+    
+    Process *process = m_exe_ctx.GetProcessPtr();
+    if (!process)
+    {
+        Target *target = m_exe_ctx.GetTargetPtr();
+        if (!target)
+        {
+            target = m_interpreter.GetDebugger().GetSelectedTarget().get();
+        }
+        if (target)
+            process = target->GetProcessSP().get();
+    }
+
+    if (process)
+        return process->GetThreadList().GetSelectedThread().get();
+    else
+        return nullptr;
+}
+
 bool
 CommandObjectParsed::Execute (const char *args_string, CommandReturnObject &result)
 {
diff --git a/lldb/source/Plugins/InstrumentationRuntime/AddressSanitizer/AddressSanitizerRuntime.cpp b/lldb/source/Plugins/InstrumentationRuntime/AddressSanitizer/AddressSanitizerRuntime.cpp
index 5cb9edb7e5f3..c66e55dd4365 100644
--- a/lldb/source/Plugins/InstrumentationRuntime/AddressSanitizer/AddressSanitizerRuntime.cpp
+++ b/lldb/source/Plugins/InstrumentationRuntime/AddressSanitizer/AddressSanitizerRuntime.cpp
@@ -173,7 +173,7 @@ AddressSanitizerRuntime::RetrieveReportData()
     if (!process_sp)
         return StructuredData::ObjectSP();
 
-    ThreadSP thread_sp = process_sp->GetThreadList().GetSelectedThread();
+    ThreadSP thread_sp = process_sp->GetThreadList().GetExpressionExecutionThread();
     StackFrameSP frame_sp = thread_sp->GetSelectedFrame();
     
     if (!frame_sp)
diff --git a/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.cpp b/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.cpp
index f57eb9e92ebf..430fbaed54d4 100644
--- a/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.cpp
+++ b/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.cpp
@@ -1229,7 +1229,7 @@ AppleObjCRuntimeV2::UpdateISAToDescriptorMapDynamic(RemoteNXMapTable &hash_table
     
     ExecutionContext exe_ctx;
     
-    ThreadSP thread_sp = process->GetThreadList().GetSelectedThread();
+    ThreadSP thread_sp = process->GetThreadList().GetExpressionExecutionThread();
     
     if (!thread_sp)
         return false;
@@ -1473,7 +1473,7 @@ AppleObjCRuntimeV2::UpdateISAToDescriptorMapSharedCache()
     
     ExecutionContext exe_ctx;
     
-    ThreadSP thread_sp = process->GetThreadList().GetSelectedThread();
+    ThreadSP thread_sp = process->GetThreadList().GetExpressionExecutionThread();
     
     if (!thread_sp)
         return DescriptorMapUpdateResult::Fail();
diff --git a/lldb/source/Plugins/MemoryHistory/asan/MemoryHistoryASan.cpp b/lldb/source/Plugins/MemoryHistory/asan/MemoryHistoryASan.cpp
index c57519871624..21e4680e4686 100644
--- a/lldb/source/Plugins/MemoryHistory/asan/MemoryHistoryASan.cpp
+++ b/lldb/source/Plugins/MemoryHistory/asan/MemoryHistoryASan.cpp
@@ -148,7 +148,7 @@ MemoryHistoryASan::GetHistoryThreads(lldb::addr_t address)
     ProcessSP process_sp = m_process_wp.lock();
     if (process_sp)
     {
-        ThreadSP thread_sp = process_sp->GetThreadList().GetSelectedThread();
+        ThreadSP thread_sp = process_sp->GetThreadList().GetExpressionExecutionThread();
 
         if (thread_sp)
         {
diff --git a/lldb/source/Plugins/Platform/POSIX/PlatformPOSIX.cpp b/lldb/source/Plugins/Platform/POSIX/PlatformPOSIX.cpp
index 031b0005a91b..72fc86ffbe26 100644
--- a/lldb/source/Plugins/Platform/POSIX/PlatformPOSIX.cpp
+++ b/lldb/source/Plugins/Platform/POSIX/PlatformPOSIX.cpp
@@ -867,7 +867,7 @@ PlatformPOSIX::EvaluateLibdlExpression(lldb_private::Process* process,
             return error;
     }
 
-    ThreadSP thread_sp(process->GetThreadList().GetSelectedThread());
+    ThreadSP thread_sp(process->GetThreadList().GetExpressionExecutionThread());
     if (!thread_sp)
         return Error("Selected thread isn't valid");
 
diff --git a/lldb/source/Plugins/Process/Utility/InferiorCallPOSIX.cpp b/lldb/source/Plugins/Process/Utility/InferiorCallPOSIX.cpp
index ebeba8c46a74..08a1ee74f2d1 100644
--- a/lldb/source/Plugins/Process/Utility/InferiorCallPOSIX.cpp
+++ b/lldb/source/Plugins/Process/Utility/InferiorCallPOSIX.cpp
@@ -43,7 +43,7 @@ lldb_private::InferiorCallMmap (Process *process,
                                 addr_t fd,
                                 addr_t offset)
 {
-    Thread *thread = process->GetThreadList().GetSelectedThread().get();
+    Thread *thread = process->GetThreadList().GetExpressionExecutionThread().get();
     if (thread == NULL)
         return false;
 
@@ -144,7 +144,7 @@ lldb_private::InferiorCallMunmap (Process *process,
                                   addr_t addr,
                                   addr_t length)
 {
-   Thread *thread = process->GetThreadList().GetSelectedThread().get();
+   Thread *thread = process->GetThreadList().GetExpressionExecutionThread().get();
    if (thread == NULL)
        return false;
    
@@ -219,7 +219,7 @@ lldb_private::InferiorCall (Process *process,
                             addr_t &returned_func,
                             bool trap_exceptions)
 {
-    Thread *thread = process->GetThreadList().GetSelectedThread().get();
+    Thread *thread = process->GetThreadList().GetExpressionExecutionThread().get();
     if (thread == NULL || address == NULL)
         return false;
 
diff --git a/lldb/source/Plugins/SystemRuntime/MacOSX/SystemRuntimeMacOSX.cpp b/lldb/source/Plugins/SystemRuntime/MacOSX/SystemRuntimeMacOSX.cpp
index 1097ef36960e..37af5b830197 100644
--- a/lldb/source/Plugins/SystemRuntime/MacOSX/SystemRuntimeMacOSX.cpp
+++ b/lldb/source/Plugins/SystemRuntime/MacOSX/SystemRuntimeMacOSX.cpp
@@ -486,7 +486,7 @@ SystemRuntimeMacOSX::GetExtendedBacktraceThread (ThreadSP real_thread, ConstStri
         }
         else
         {
-            ThreadSP cur_thread_sp (m_process->GetThreadList().GetSelectedThread());
+            ThreadSP cur_thread_sp (m_process->GetThreadList().GetExpressionExecutionThread());
             AppleGetThreadItemInfoHandler::GetThreadItemInfoReturnInfo ret = m_get_thread_item_info_handler.GetThreadItemInfo (*cur_thread_sp.get(), real_thread->GetID(), m_page_to_free, m_page_to_free_size, error);
             m_page_to_free = LLDB_INVALID_ADDRESS;
             m_page_to_free_size = 0;
@@ -524,7 +524,7 @@ SystemRuntimeMacOSX::GetExtendedBacktraceFromItemRef (lldb::addr_t item_ref)
     ThreadSP return_thread_sp;
 
     AppleGetItemInfoHandler::GetItemInfoReturnInfo ret;
-    ThreadSP cur_thread_sp (m_process->GetThreadList().GetSelectedThread());
+    ThreadSP cur_thread_sp (m_process->GetThreadList().GetExpressionExecutionThread());
     Error error;
     ret = m_get_item_info_handler.GetItemInfo (*cur_thread_sp.get(), item_ref, m_page_to_free, m_page_to_free_size, error);
     m_page_to_free = LLDB_INVALID_ADDRESS;
@@ -696,7 +696,7 @@ SystemRuntimeMacOSX::PopulateQueueList (lldb_private::QueueList &queue_list)
     if (BacktraceRecordingHeadersInitialized())
     {
         AppleGetQueuesHandler::GetQueuesReturnInfo queue_info_pointer;
-        ThreadSP cur_thread_sp (m_process->GetThreadList().GetSelectedThread());
+        ThreadSP cur_thread_sp (m_process->GetThreadList().GetExpressionExecutionThread());
         if (cur_thread_sp)
         { 
             Error error;
@@ -760,7 +760,7 @@ SystemRuntimeMacOSX::GetPendingItemRefsForQueue (lldb::addr_t queue)
 {
     PendingItemsForQueue pending_item_refs;
     AppleGetPendingItemsHandler::GetPendingItemsReturnInfo pending_items_pointer;
-    ThreadSP cur_thread_sp (m_process->GetThreadList().GetSelectedThread());
+    ThreadSP cur_thread_sp (m_process->GetThreadList().GetExpressionExecutionThread());
     if (cur_thread_sp)
     { 
         Error error;
@@ -859,7 +859,7 @@ SystemRuntimeMacOSX::CompleteQueueItem (QueueItem *queue_item, addr_t item_ref)
 {
     AppleGetItemInfoHandler::GetItemInfoReturnInfo ret;
 
-    ThreadSP cur_thread_sp (m_process->GetThreadList().GetSelectedThread());
+    ThreadSP cur_thread_sp (m_process->GetThreadList().GetExpressionExecutionThread());
     Error error;
     ret = m_get_item_info_handler.GetItemInfo (*cur_thread_sp.get(), item_ref, m_page_to_free, m_page_to_free_size, error);
     m_page_to_free = LLDB_INVALID_ADDRESS;
diff --git a/lldb/source/Target/StopInfo.cpp b/lldb/source/Target/StopInfo.cpp
index a7b1b8eeeb27..7c244363ffd2 100644
--- a/lldb/source/Target/StopInfo.cpp
+++ b/lldb/source/Target/StopInfo.cpp
@@ -371,6 +371,10 @@ protected:
                     // running all the callbacks.
 
                     m_should_stop = false;
+                    
+                    // We don't select threads as we go through them testing breakpoint conditions and running commands.
+                    // So we need to set the thread for expression evaluation here:
+                    ThreadList::ExpressionExecutionThreadPusher thread_pusher(thread_sp);
 
                     ExecutionContext exe_ctx (thread_sp->GetStackFrameAtIndex(0));
                     Process *process  = exe_ctx.GetProcessPtr();
diff --git a/lldb/source/Target/ThreadList.cpp b/lldb/source/Target/ThreadList.cpp
index a34cb0fa143a..3dc37f1fa0e0 100644
--- a/lldb/source/Target/ThreadList.cpp
+++ b/lldb/source/Target/ThreadList.cpp
@@ -71,6 +71,30 @@ ThreadList::~ThreadList()
     Clear();
 }
 
+lldb::ThreadSP
+ThreadList::GetExpressionExecutionThread()
+{
+    if (m_expression_tid_stack.empty())
+        return GetSelectedThread();
+    ThreadSP expr_thread_sp = FindThreadByID(m_expression_tid_stack.back());
+    if (expr_thread_sp)
+        return expr_thread_sp;
+    else
+        return GetSelectedThread();
+}
+
+void
+ThreadList::PushExpressionExecutionThread(lldb::tid_t tid)
+{
+    m_expression_tid_stack.push_back(tid);
+}
+    
+void
+ThreadList::PopExpressionExecutionThread(lldb::tid_t tid)
+{
+    assert(m_expression_tid_stack.back() == tid);
+    m_expression_tid_stack.pop_back();
+}
 
 uint32_t
 ThreadList::GetStopID () const
@@ -828,3 +852,16 @@ ThreadList::GetMutex ()
     return m_process->m_thread_mutex;
 }
 
+ThreadList::ExpressionExecutionThreadPusher::ExpressionExecutionThreadPusher (lldb::ThreadSP thread_sp) :
+    m_thread_list(nullptr),
+    m_tid(LLDB_INVALID_THREAD_ID)
+{
+    if (thread_sp)
+    {
+        m_tid = thread_sp->GetID();
+        m_thread_list = &thread_sp->GetProcess()->GetThreadList();
+        m_thread_list->PushExpressionExecutionThread(m_tid);
+    }
+}
+
+