A thorough introduction to Borel sets and measurable selections, acting as a stepping stone to descriptive set theory by presenting such important techniques as universal sets, prewellordering, scales, etc. It contains significant applications to other branches of mathematics and serves as a self-contained reference accessible by mathematicians in many different disciplines. Written in an easily understandable style, and using only naive set theory, general topology, analysis, and algebra, it is thus well suited for graduates exploring areas of mathematics for their research and for those requiring Borel sets and measurable selections in their work.