How to implement a circle button in XAML

 <Button  Width="100" Height="100" Content="Abcd">
        <Button.Template>
            <ControlTemplate TargetType="{x:Type Button}">
                <Grid>
                <Ellipse Fill="Red"/>
                    <ContentPresenter Content="{TemplateBinding Content}" HorizontalAlignment="Center" VerticalAlignment="Center"/>
                </Grid>
            </ControlTemplate>
        </Button.Template>
    </Button>

you must set the height and width of button same for it to be Circle.

This is a very quick way to do it. It can be changed into a style and it could be made more flexible by creating a TemplatedControl allowing the designer to easily change the colors and other properties.

<Button Width="100"
        Height="100">
    <Button.Template>
        <ControlTemplate TargetType="Button">
            <Grid>
                <Ellipse Stroke="Black"
                         StrokeThickness="2">
                    <Ellipse.Fill>
                        <RadialGradientBrush>
                            <GradientStop Offset="0"
                                          Color="Lime" />
                            <GradientStop Offset="1"
                                          Color="Lime" />
                            <GradientStop Offset="1"
                                          Color="Gold" />
                            <RadialGradientBrush.Transform>
                                <TransformGroup>
                                    <ScaleTransform ScaleY="0.65" />
                                </TransformGroup>
                            </RadialGradientBrush.Transform>
                        </RadialGradientBrush>
                    </Ellipse.Fill>
                </Ellipse>
                <ContentPresenter HorizontalAlignment="Center"
                                  VerticalAlignment="Center"/>
            </Grid>
        </ControlTemplate>
    </Button.Template>
</Button>