Jesus' Brothers (Matthew 12:46) What exactly did Matthew mean when he is talking about Jesus' brothers in Matthew 12:46? From Matthew 12:49, its clear that he didn't mean Jesus' disciples as his brothers. So who are the Jesus' brothers mentioned there?
In Protestant Christianity, it is understood that Mary was a virgin until the birth of Jesus, but not after.  


  24 When Joseph woke from sleep, he did as the angel of the Lord
  commanded him: he took his wife, 25 but knew her not until she had
  given birth to a son. And he called his name Jesus.  Matthew 1:24-25
  ESV


After the birth of Jesus, then, Joseph and Mary were like any other married couple and would have likely had other children.

Paul refers to someone named "James" whom he refers to as "the Lord's brother".


  But I saw none of the other apostles except James the Lord's brother.  Galatians 1:19 ESV


Later in Matthew, Jesus arrives in Nazareth, and he is rejected there because that is where he grew up, and people refused to believe he was anything special.  They specifically say that we know his father (who was actually only his stepfather), his mother Mary, and four named brothers.


  Is not this the carpenter's son? Is not his mother called Mary? And
  are not his brothers James and Joseph and Simon and Judas? And are not all his sisters with us? Where then did this man get all these things? Matthew 13:55-56 ESV


So, Jesus appears to have had four brothers, namely James, Joseph, Simon and Judas.  It also indicates that Jesus had sisters, but it does not give a specific number.