A method for questioning and answering applied at a questioner client, comprising: receiving a message input by a user; characterized in that the method further comprises: sending the message to a question-and-answer server such that the question-and-answer server sends the message to one or more answerer clients whose user tags are matched with key words in the message; and in response to the users of the one or more answerer clients whose user tags are matched with the key words in the message joining into an instant messaging session group established by the question-and-answer server for the user of the questioner client for the message, entering into an instant messaging session with the users of the one or more answerer clients whose user tags are matched with the key words in the message through the instant messaging session group so as to obtain a reply message from the users of the one or more answerer clients whose user tags are matched with the key words in the message through the instant messaging session, and wherein the instant messaging session group comprises the one or more answerer clients whose user tags are matched with the key words in the message. receiving a message input by a user; characterized in that the method further comprises: sending the message to a question-and-answer server such that the question-and-answer server sends the message to one or more answerer clients whose user tags are matched with key words in the message; and in response to the users of the one or more answerer clients whose user tags are matched with the key words in the message joining into an instant messaging session group established by the question-and-answer server for the user of the questioner client for the message, entering into an instant messaging session with the users of the one or more answerer clients whose user tags are matched with the key words in the message through the instant messaging session group so as to obtain a reply message from the users of the one or more answerer clients whose user tags are matched with the key words in the message through the instant messaging session, and wherein the instant messaging session group comprises the one or more answerer clients whose user tags are matched with the key words in the message. sending the message to a question-and-answer server such that the question-and-answer server sends the message to one or more answerer clients whose user tags are matched with key words in the message; and in response to the users of the one or more answerer clients whose user tags are matched with the key words in the message joining into an instant messaging session group established by the question-and-answer server for the user of the questioner client for the message, entering into an instant messaging session with the users of the one or more answerer clients whose user tags are matched with the key words in the message through the instant messaging session group so as to obtain a reply message from the users of the one or more answerer clients whose user tags are matched with the key words in the message through the instant messaging session, and wherein the instant messaging session group comprises the one or more answerer clients whose user tags are matched with the key words in the message.