This agriculture extension service publication from Pennsylvania State University is an introduction to weed control and herbicide use. An initial discussion of the characteristics of weeds includes scientific naming, weed competition with crops, weed dispersal and dormancy, and conditions affecting weed seed germination. The main body of the publication discusses herbicides. In this discussion topics included are: (1) growth-regulating herbicides; (2) contact herbicides; (3) chemical structure of herbicides; (4) herbicide formulations; (5) herbicide safety; (6) herbicide toxicity; and (7) factors affecting herbicide persistance. This publication could also be useful to people other than agricultural pesticide applicators. (MR)