How to create a Multiline TextBox in WPF

Setting the TextWrapping attribute to Wrap will cause entered text to wrap to a new line when the edge of the TextBox control is reached, automatically expanding the TextBox control to include room for a new line, if necessary.

Setting the AcceptsReturn attribute to true causes a new line to be inserted when the RETURN key is pressed, once again automatically expanding the TextBox to include room for a new line, if necessary.

The VerticalScrollBarVisibility attribute adds a scroll bar to the TextBox, so that the contents of the TextBox can be scrolled through if the TextBox expands beyond the size of the frame or window that encloses it.

<TextBox
  Name="tbMultiLine"
  TextWrapping="Wrap"
  AcceptsReturn="True"
  VerticalScrollBarVisibility="Visible"
>
  This TextBox will allow the user to enter multiple lines of text.  When the RETURN key is pressed, 
  or when typed text reaches the edge of the text box, a new line is automatically inserted.
</TextBox>