A Recursive K-Nearest Neighbors(RKNN) algorihm for recommender systems. Developed for my diploma thesis at Department of Financial and Management Engineering, University of Aegean. RKNN overcomes the limitation of the conventional KNN algorithm, which sometimes is unable to find similarities for a (user,item) pair, by recursively making predictions to the neighbors of the user for the asked item. Then, these predictions can be used to make a prediction for the (user, item) pair.