It comes first, but it is written last. The abstract should summarize the paper: it should mention the material and/or study area, it should mention the methods, it should summarize the results, and it should present the main conclusions. The first sentence should probably put forth the most striking result or conclusion, so that the reader will keep reading. That all sounds like a lot, but a good first sentence can actually do most of the work, or at least get it started. For example: Atomic adsorption analyses of 54 avocados sampled from groves in Florida and Georgia, coupled with previously published groundwater analyses, show that . . . . . This first sentence gets its material and methods into the subject, with the main conclusion to follow in the predicate. Further sentences can then go into the details and/or elaborate the significance of the conclusions. This formulaic approach to the first sentence can save an author hours of head-pounding to craft the most important ten to thirty words in the entire paper. You may have read, or perhaps will read, abstracts written in a European style that goes like this: Avocados from groves in Florida and Georgia were studied by means of atomic adsorption analyses, and these results, coupled with previously published groundwater analyses, lead to a number of interesting inferences. This tells the reader very little and should not be imitated. (L.B. Railsback and Mumpton F.A)