We offer three articles in this edition of Problems and Techniques, describing optimal radiation therapy strategies, calculating Green's functions in the complex plane, and finding the zeros of complex functions by inverting their asymptotic approximations. Radiation therapy is a long-standing tool for treating cancer patients. The goal is to kill tumor cells by bombarding them with beams of radiation while minimizing damage to healthy cells that are in the beam's path. The authors of our first article, David Shepard, Michael Ferris, Gustavo Olivera, and Thomas Mackie, examine a new technique called ``tomotherapy,' which delivers beams of radiation from points normal to a circular arc around the patient's body in much the same fashion that computed tomography (CT) constructs images. The radiation beam is delivered in narrow slits that affect only a small slice of the patient. The patient lies on a couch that, like a CT apparatus, can be moved into and out of the radiation field. The mathematical challenge is to find an optimal delivery strategy that, for example, minimizes the total radiation to the patient while delivering a lethal dose to the tumor. The authors present several optimization problems and solution techniques. If you would like to have a go at figuring dosages, their software and data are available on a web site. Our second article, by Mark Embree and Nick Trefethen, involves computing the Green's function in the complex plane in a domain exterior to a set of symmetric regions relative to and on the real axis. The symmetric configuration leads to a simple solution for the Green's function through a sequence of Schwarz--Christoffel conformal maps. Several nice examples illustrate both the process and the results. Applications are presented in potential theory and polynomial approximation, with the latter involving several interesting minimax problems that can be solved by exploiting their relationship to the Green's function. The polynomial approximations may be used in, e.g., signal processing and Krylov iteration. Our third article, by Bruce Fabijonas and Frank Olver, is another feature for fans of complex analysis and approximation theory. The goal here is a technique for finding the zeros of complex functions that are known near singularities through asymptotic approximations. After reviewing the relevant theory, the authors show how to construct asymptotic expansions of functions and their zeros. Airy functions are used to test the theory and expansions are generated for them, their first derivatives, their zeros, and their stationary points. Software for symbolic computation is available for use by those who want to try their hand. Bounds on the accuracy of the results are discussed, and the authors suggest a conjecture for us to prove. Although the subject matter in this installment of Problems and Techniques is pretty far removed from my domain of influence, I thoroughly enjoyed all of the articles. I hope that you will too. Please join me in thanking all of our authors for their fine contributions.