Excel: count cells in which text appears

I have two columns of data. The second column has various text strings, and I want to count the number of cells in which a certain text appears. Some cells may contain "Yes, I'll attend," or "Yes, I'll be there," and I want to count how many cells have the word "Yes" in them. COUNT and COUNTIF look for precise matches. Is there any way I can count based on a partial match?