[reaction: see text] [cis-Ru(II)(dmp)2(H2O)2]2+ (dmp = 2,9-dimethylphenanthroline) was found to be a selective oxidation catalyst using hydrogen peroxide as oxidant. Thus, primary alkenes were very efficiently oxidized via direct carbon-carbon bond cleavage to the corresponding aldehydes as an alternative to ozonolysis. Secondary alkenes were much less reactive, leading to regioselective oxidation of substrates such as 4-vinylcyclohexene and 7-methyl-1,6-octadiene at the terminal position. Primary allylic alcohols were chemoselectively oxidized to the corresponding allylic aldehydes, e.g., geraniol to citral.