Holmstrom Algebraic space

Algebraic stacks may be viewed as groupoid objects in the category of algebraic spaces. (Joshua: The intersection cohomology…)

nLab

http://mathoverflow.net/questions/3194/what-are-the-benefits-of-using-algebraic-spaces-over-schemes

See Toen course in cours folder under Toen, I think around chapters 2 to 4-2 in particular.

http://mathoverflow.net/questions/11226/commutative-rings-to-algebraic-spaces-in-one-jump

nLab page on Algebraic space