The past several years have seen an increased interest in the use of toxic weapons -- i.e., weapons that incorporate inexpensive and easily attained chemicals and industrial waste -- on the part of both state and nonstate entities. Such weapons have been sought out by virtue of their abundance and ready availability and because they allow hostile entities to improve their capabilities within the context of symmetrical warfare. Despite these trends, however, the level of threat such weapons represent has yet to be precisely determined. Accordingly, this report seeks to provide a qualitative overview of the threat toxic weapons pose as well as to identify key vulnerabilities the United States and the U.S. military face. Toward this goal, the report describes the composition and sources of toxic weapons as well as their potential for harm, and it then outlines the use of such weapons by state and nonstate actors over the past decade. Following this analysis, the report focuses on the implications of toxic weapon use both for U.S. forces engaged in military operations and for the U.S. homeland. The author concludes that toxic warfare must be better understood so that the threat can be more effectively incorporated into military and civilian crisis response planning.