A stereoselective reaction forms one stereoisomer preferentially over another stereoisomer. In this reaction for reaction stereoisomerism may or may not possible. A reaction is stereospecific if the reactant can exist as stereoisomers and each stereoisomers of reactant forms a different stereoisomer or a different set of stereoisomers of the product.
All stereospecific reaction are stereoselective but a stereoselective reaction may or may not stereospecific. 

	LIST-I (Reaction)		LIST-II(Nature of reaction)		LIST-III (major product)
I)		A)	Stereospecific	P)	Erythro isomer
II)		B)	Stereoselective	Q)	Threo isomer
III)		C)	Regioselective	R)	Meso
IV)		D)	Only syn addition	S)	Racemic mixture