In MainWindow the commandbinding works fine. In UserControl1 it doesnt work. Note the datacontext is set correctly as is evidenced by the content of the button which is the result of a binding.

I am not trying to bind the command in the usercontrol to a command in mainwindow or any other such trickery. I am just trying to replicate what I did in MainWindow in UserControl1.

// MainWindow xaml
<StackPanel>
    <Button Content="Click Here" Command="{Binding ClickHereCommand}" Height="25" Width="90"></Button>
    <local:UserControl1></local:UserControl1>
</StackPanel>

// MainWindow

public partial class MainWindow : Window
{
    public static RoutedCommand ClickHereCommand { get; set; }

    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = this;
        ClickHereCommand = new RoutedCommand();
        CommandBindings.Add(new CommandBinding(ClickHereCommand, ClickHereExecuted));
    }

    public void ClickHereExecuted(object sender, ExecutedRoutedEventArgs e)
    {
        System.Windows.MessageBox.Show("hello");
    }
}


// UserControl1 xaml
<UserControl x:Class="CommandBindingTest.UserControl1"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         mc:Ignorable="d" 
         d:DesignHeight="300" d:DesignWidth="300" x:Name="root">

<Grid DataContext="{Binding ElementName=root}" >
    <Button Content="{Binding ButtonContent}" Command="{Binding ClickHereCommand}" Height="25" Width="90"></Button>
</Grid>
</UserControl>

// UserControl1

public partial class UserControl1 : UserControl, INotifyPropertyChanged
{
    private string _ButtonContent;
    public string ButtonContent
    {
        get { return _ButtonContent; }
        set
        {
            if (_ButtonContent != value)
            {
                _ButtonContent = value;
                OnPropertyChanged("ButtonContent");
            }
        }
    }

    public static RoutedCommand ClickHereCommand { get; set; }


    public UserControl1()
    {
        InitializeComponent();
        ClickHereCommand = new RoutedCommand();
        CommandBindings.Add(new CommandBinding(ClickHereCommand, ClickHereExecuted));
        ButtonContent = "Click Here";
    }

    public void ClickHereExecuted(object sender, ExecutedRoutedEventArgs e)
    {
        System.Windows.MessageBox.Show("hello from UserControl1");
    }


    #region INotifyPropertyChanged Members
    public event PropertyChangedEventHandler PropertyChanged;

    public void OnPropertyChanged(string name)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(name));
        }
    }
    #endregion
}