His research interests include lifelong and continual learning, sentiment analysis, lifelong learning chatbots, open-world AI/learning, natural language processing (NLP), and data mining and machine learning. He has published extensively in top conferences and journals (his Google Scholar page). He also authored five books: one about lifelong machine learning (first ever book on the topic), one about lifelong learning dialogue systems (first ever book on the topic), two about sentiment analysis, and one about Web mining. Three of his papers received Test-of-Time awards: two from SIGKDD (ACM Special Interest Group on Knowledge Discovery and Data Mining) and one from WSDM (ACM International Conference on Web Search and Data Mining). Another of his papers received Test-of-Time award - honorable mention also from WSDM. Some of his work has been widely reported in the international press, including a front-page article in the New York Times. On professional services, he has served as the Chair of ACM SIGKDD from 2013-2017, as program chair of many leading data mining conferences, including KDD, ICDM, CIKM, WSDM, SDM, and PAKDD, as associate editor of leading journals such as TKDE, TWEB, DMKD and TKDD, and as area chair or senior PC member of numerous NLP, AI, Web, and data mining conferences. He is a recipient of ACM SIGKDD Innovation Award (the most prestigious technical achievement award from SIGKDD), and he is a Fellow of the ACM, AAAI, and IEEE.