The possibility of offsetting greenhouse gas warming by introducing artificial aerosols into the stratosphere to increase the Earth's albedo has been widely discussed, but little attention has been given to the details of its implementation. It is usually assumed that the aerosols would be sulfuric acid droplets (hydrated sulfur trioxide), like natural volcanic aerosols. Other materials may be more advantageous, but sophisticated “engineered” particles probably cannot be produced in sufficient quantity. I consider a variety of possible injection vehicles. Aircraft are unlikely to have sufficient lift capability to the necessary altitudes, guns are inefficient, and exotic methods like balloons and chimneys face daunting difficulties. Simple rockets are proven and economical, and can deliver material to any desired altitude. Artificial injection begins at a much higher aerosol (or precursor) density than a volcanic plume, raising novel issues of chemical kinetics and particle agglomeration. Detailed experimental and theoretical investigation are required to establish the feasibility of stratospheric aerosol geoengineering. An appendix argues that natural, as well as anthropogenic, climate change may pose challenges that could be met by these methods.