This chapter first introduces the background and development of information filtering and then analyzes the reasons for the emergence of information filtering technology. Based on applications, it presents focused information filtering, information filtering recommendations, and their cutting-edge applications according to different application scenarios, analyzes focused information filtering mainly based on text and images, explains the two classic focused information filtering algorithms based on black and white list filtering and content filtering, introduces the three methods commonly used in video recommendation systems: content filtering, collaborative filtering, and hybrid filtering, mainly focusing on algorithm standards and feature descriptions, and introduces the application range and cutting-edge technology of the above filtering technologies and algorithms, and finally presents specific experimental examples.