Contract-based programming is a software development technique, where you include assertions of program properties as a part of the compiled source text. In the strict form, the assertions are checked at compile-time, but in this presentation I will focus on the more common, less strict, form, where at least some of the assertions aren't checked until run-time. Ada gives us a lot of help, so we can write the our assertions about the program properties once, and then have the compiler insert actual run-time checks wherever there is a possibility that the assertion is violated.