--MainWindow.xaml
<Window x:Class="WPFTestProject.MainWindow"
        x:Name="MainDialog"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:us="clr-namespace:WPFTestProject"
        Title="MainWindow" Height="200" Width="350">

    <Grid>
        <Grid.Effect>
            <BlurEffect Radius="{Binding BlurRadius}" />
        </Grid.Effect>
        <TabControl ItemsSource="{Binding Tabs}" SelectedItem="{Binding SelectedTab}">
            <TabControl.ItemContainerStyle>
                <Style TargetType="TabItem">
                    <Setter Property="Header" Value="{Binding Header}" />
                </Style>
            </TabControl.ItemContainerStyle>
            <TabControl.Resources>
                <!-- TODO: Need to add two more DataTemplates here once the second and third tabs are implemented -->
                <DataTemplate DataType="{x:Type us:FirstTabViewModel}">
                    <us:FirstTabUserControl />
                </DataTemplate>
                <DataTemplate DataType="{x:Type us:SecondTabViewModel}">
                    <us:SecondTabUserControl />
                </DataTemplate>
            </TabControl.Resources>
        </TabControl>
    </Grid>
</Window>

--MainWindowViewModel.cs
using System.Collections.ObjectModel;

namespace WPFTestProject
{
    public interface ITab
    {
        string Header { get; set; }
    }

    public class MainWindowViewModel : ObservableObject
    {
        private double _blurRadius;
        public double BlurRadius
        {
            get { return _blurRadius; }
            set
            {
                _blurRadius = value;
                RaisePropertyChanged( "BlurRadius" );
            }
        }

        private ObservableCollection<ITab> _tabs;
        public ObservableCollection<ITab> Tabs
        {
            get { return _tabs; }
            set
            {
                _tabs = value;
                RaisePropertyChanged( "Tabs" );
            }
        }

        private ITab _selectedTab;
        public ITab SelectedTab
        {
            get
            {
                return _selectedTab;
            }
            set
            {
                _selectedTab = value;
                RaisePropertyChanged( "SelectedTab" );
            }
        }

        public MainWindowViewModel()
        {
            // Start off with no blur
            this.BlurRadius = 0;

            this.Tabs = new ObservableCollection<ITab>();
            this.Tabs.Add( new FirstTabViewModel() { Header = "First Tab" } );
            this.Tabs.Add( new SecondTabViewModel() { Header = "Second Tab" } );
            this.SelectedTab = this.Tabs[ 0 ];
        }
    }
}

--FirstTabUserControl.xaml
<UserControl x:Class="WPFTestProject.FirstTabUserControl"
             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="200" d:DesignWidth="350">
    <Grid>
        <Button Content="Press Me! (#1)" Command="{Binding PressButtonCommand}" HorizontalAlignment="Center" VerticalAlignment="Center" Width="95" />
    </Grid>
</UserControl>


--FirstTabViewModel.cs
namespace WPFTestProject
{
    public class FirstTabViewModel : ITab
    {
        public string Header { get; set; }

        public RelayCommand PressButtonCommand { get; set; }

        public FirstTabViewModel()
        {
            this.PressButtonCommand = new RelayCommand( this.HandleButtonPress, () => true );
        }

        private void HandleButtonPress()
        {

        }
    }
}