This is a final call for participation for the Fields Institute Workshop on semigroups and categories, to be held in Ottawa, May 2-4 2010. The focus of the workshop is on the connections between category theory and semigroup theory, as well as the relations to (etale) groupoids, locales, categories of partial maps and C*-algebras. Local information can be found on the following web page: http://www.mathstat.uottawa.ca/~phofstra/semigroup10/workshop.html In case there are questions, do not hesitate to contact one of the organizers. [For admin and other information see: http://www.mta.ca/~cat-dist/ ]