Chapter ?? of CRC Handbook on Algorithms and Theory of Computation, CRC Press (1999), co-authored with Phil Klein.
A 20-page sketch of basic techniques and terms in the design and analysis of combinatorial approximation algorithms.
Sections: Introduction, Underlying principles, Approximation algorithms with small additive error, Performance guarantees, Randomized rounding and linear programming, Performance ratios and c-approximation, Polynomial approximation schemes, Constant-factor performance guarantees, Logarithmic performance guarantees, Multi-criteria problems, Hard-to-approximate problems, Research Issues and Summary, Defining Terms, Further Information.