Collaborative filtering and content-based filtering are two types of information filtering techniques. Combining these two techniques can improve the recommendation effectiveness. The main problem with previous research is that the content information and the rating information are not combined in an integrated way. This paper presents a unified probabilistic framework that allows the mutual interaction between these two types of information. Experiments have shown that the new unified filtering algorithm outperforms a pure collaborative filtering approach, a pure content-based filtering approach and another unified filtering algorithm. Categories and Subject Descriptors H.3.3 [Information Search and Retrieval]: Filtering General Terms Algorithms Keywords Unified filtering