ContentsI. Introduction 473 II. Peptides-on-Pins 474 A. Method 474 B. Applications 476 III. Macroscopic DNA Arrays 478 A. Method 478 B. Applications 479 IV. Light-Directed Synthesis 480 A. Background 480 B. Method 480 C. Applications 483 1. Peptides 483 2. DNA 484 V. Peptides on Paper 485 A. Method 485 B. Applications 486 VI. Inorganic Combinatorial Libraries 486 A. Method 486 B. Applications 487 VII. Conclusions 487 VIII. References and Notes 487Michael Pirrung (b. 1955) grew up in the rodeo capital of Texas, Mesquite. After graduating from the University of TexassAustin, he pursued a Ph.D. at UC-Berkeley. He did research on stereoselective aldol condensations with Clayton Heathcock and an independent project on a photochemical total synthesis of isocomene. After a postdoc with Gilbert Stork at Columbia, he took a position at Stanford. His group became known for work on the mechanism of the biosynthesis of ethylene, the plant-ripening hormone. In 1988, he joined a "working group" of scientists meeting in Palo Alto to form a then-new company, Affymax. He established the chemistry program at Affymax, focusing on methods of creating chemical diversity. His work there on light-directed synthesis was recognized with the AAAS-Newcomb Cleveland Prize. In 1990, he moved to Duke University where he is now Professor of Chemistry and Director of the Program in Biological Chemistry. He has published ∼100 peer-reviewed articles and holds several patents. A sabbatical at the Baylor College of Medicine in 1995 resulted in one current interest, chip-based comparison sequencing for mutation detection in highly mutated disease genes.Continuing interests include asymmetric catalysis, synthetic methodology, total synthesis, photochemistry, enzymology, combinatorial chemistry, lightdirected synthesis, and ethylene biosynthesis.