I'm attempting to build a very simple wxPython GUI that monitors and displays external data. There is a button that turns the monitoring on/off. When monitoring is turned on, the GUI updates a couple of wx StaticLabels with real-time data. When monitoring is turned off, the GUI idles. The way I tried to build it was with a fairly simple Python Thread layout. When the 'Start Monitoring' button is clicked, the program spawns a thread that updates the labels with real-time information. When the 'Stop Monitoring' button is clicked, thread.join() is called, and it should stop. The start function works and the real-time data updating works great, but when I click 'Stop', the whole program freezes. I'm running this on Windows 7 64-bit, so I get the usual "This Program has Stopped Responding" Windows dialog. Here is the relevant code: class MonGUI(wx.Panel): def __init__(self, parent): wx.Panel.__init__(self, parent) ... ... other code for the GUI here ... ... # Create the thread that will update the VFO information self.monThread = Thread(None, target=self.monThreadWork) self.monThread.daemon = True self.runThread = False def monThreadWork(self): while self.runThread: ... ... Update the StaticLabels with info ... (This part working) ... # Turn monitoring on/off when the button is pressed. def OnClick(self, event): if self.isMonitoring: self.button.SetLabel("Start Monitoring") self.isMonitoring = False self.runThread = False self.monThread.join() else: self.button.SetLabel("Stop Monitoring") self.isMonitoring = True # Start the monitor thread! self.runThread = True self.monThread.start() I'm sure there is a better way to do this, but I'm fairly new to GUI programming and Python threads, and this was the first thing I came up with. So, why does clicking the button to stop the thread make the whole thing freeze up?