Well after fiddling with MVVM light to get my button to enable and disable when I want it to... I sort of mashed things together until it worked. However, I just know I'm doing something wrong here. I have RaiseCanExecuteChanged and CanExecute in the same area being called. Surely this is not how it's done? Here's my xaml <Button Margin="10, 25, 10, 25" VerticalAlignment="Center" HorizontalAlignment="Center" Width="50" Height="50" Grid.Column="1" Grid.Row="3" Content="Host"> <i:Interaction.Triggers> <i:EventTrigger EventName="Click"> <mvvmLight:EventToCommand Command="{Binding HostChat}" MustToggleIsEnabled="True" /> </i:EventTrigger> </i:Interaction.Triggers> </Button> And here's my code public override void InitializeViewAndViewModel() { view = UnityContainer.Resolve<LoginPromptView>(); viewModel = UnityContainer.Resolve<LoginPromptViewModel>(); view.DataContext = viewModel; InjectViewIntoRegion(RegionNames.PopUpRegion, view, true); viewModel.HostChat = new DelegateCommand(ExecuteHostChat, CanHostChat); viewModel.PropertyChanged += new System.ComponentModel.PropertyChangedEventHandler(ViewModelPropertyChanged); } void ViewModelPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e) { if (e.PropertyName == "Name" || e.PropertyName == "Port" || e.PropertyName == "Address") { (viewModel.HostChat as DelegateCommand).RaiseCanExecuteChanged(); (viewModel.HostChat as DelegateCommand).CanExecute(); } } public void ExecuteHostChat() { } public bool CanHostChat() { if (String.IsNullOrEmpty(viewModel.Address) || String.IsNullOrEmpty(viewModel.Port) || String.IsNullOrEmpty(viewModel.Name)) { return false; } else return true; } See how these two are together? Surely that can't be right. I mean... it WORKS for me... but something seems wrong about it. Shouldn't RaiseCanExecuteChanged call CanExecute? It doesn't... and so if I don't have that CanExecute in there, my control never toggles its IsEnabled like I need it to. (viewModel.HostChat as DelegateCommand).RaiseCanExecuteChanged(); (viewModel.HostChat as DelegateCommand).CanExecute();