How to bind multiple values to a single WPF TextBlock?

You can use a MultiBinding combined with the StringFormat property. Usage would resemble the following:

<TextBlock>
    <TextBlock.Text>    
        <MultiBinding StringFormat="{}{0} + {1}">
            <Binding Path="Name" />
            <Binding Path="ID" />
        </MultiBinding>
    </TextBlock.Text>
</TextBlock>

Giving Name a value of Foo and ID a value of 1, your output in the TextBlock would then be Foo + 1.

Note: This is only supported in .NET 3.5 SP1 and 3.0 SP2 or later.