Recently, question and answering systems have attracted lots of attention. Given a question, the goal of question and answering is to return a concise, exact answer. According to the format of data, question and answering can be divided into three categories: the structural data based question and answering, the free-text based question and answering, the question-answer pairs based question and answering. This paper describes and summarizes the characteristics and related researches of these three categories respectively. Then, it discusses the future work of question and answering.