In this paper, we work out in detail the tadpole cancellation conditions as
well as the generalized Green-Schwarz mechanism for type IIB orientifold
compactifications with D3- and D7-branes. We find that not only the well-known
D3- and D7-tadpole conditions have to be satisfied, but in general also the
vanishing of the induced D5-brane charges leads to a non-trivial constraint. In
fact, for the case h−1,1=0 the latter condition is important for
the cancellation of chiral anomalies. We also extend our analysis by including
D9- as well as D5-branes and determine the rules for computing the chiral
spectrum of the combined system.Comment: 33+7 pages; 2 figures; v2: references added; v3: published versio