 <p>I'm going to go ahead and post this as an answer in case someone else gets stuck on this. </p> <p>When you set the <code>Width</code> and <code>Height</code> properties of the <code>TextBlock</code> control, it will first horizontally increase in size to accommodate as much text as it can <em>before</em> wrapping the text (if the <code>TextWrapping</code> property is set to Wrap). Once it decides it needs to wrap the text, if the <code>Height</code> is set to Auto, the text box will resize vertically to accommodate the text (until it hits the bottom of whatever UI container you put it in). If you do not want the text box to resize past a certain point, you will need to set values for the <code>MaxWidth</code> and <code>MaxHeight</code> properties. This will force the <code>TextBlock</code> to wrap at a certain width.</p>