All Christians that subscribe to the doctrine of the Virgin Birth believe that Joseph was Mary's husband and Jesus' guardian, but that he had no biological material from Joseph. It is a very, very widely held belief - most Evangelicals (including myself), Protestants, Catholics, and Orthodox subscribe to it, but it is not accepted by many more liberal denominations.
The idea is suggested by Isaiah, in which it was (posibly mis-)translated "Behold a Virgin shall conceive." The famous phrasing of 7:14 is "Behold, a virgin shall conceive." The immediate context, however, is a King who is being told that his enemies shall be defeated very, very soon - so soon in fact, that if a young girl gets pregnant, she will be "delievered" before the child is born. That said, by the time of the early Christians, it was popularly accepted that this also spoke of the birth of the Messiah, who would be of a girl who had not had intercourse. The Hebrew of the OT could be young maiden, but the Greek of the NT clearly presupposes a girl who had never lain with a man.
In any case, the narratives of Matthew (1:18) and Luke explicitly say that the child was put in her by the Holy Spirit, not Joseph.