The invention relates to erlotinib salts selected from the group consisting of the maleic acid salt, salicylic acid salt. L-mandelic acid alt. adipinic acid salt. 1.5-naphthalene-disulfonic acid salt. L-pyroglutamic acid salt. 1 -hydroxy-2-naphthoic acid salt, and mandelic acid salt and amorphous and crystalline forms, hydrates and solvates thereof. The erlotinib salts of the present invention are useful in therapy, particularly for the treatment or prophylaxis of non- small cell lung carcinoma and pancreas rarcinoma.