Particular Field Value Changes Every Month - How To Keep Historical Information

I have 2 tables.

Table A contains a list of Projects that evolve over time. Example:

Table A
ID Project Name Comment Comment Date
__________________________________________________ ________
1 Name 1 Comment 1.1 12/22/13
2 Name 2 Comment 2.1 12/20/13
3 Name 3 Comment 3.1 12/02/13

Now, let's say that Table A changes over time - just with the Comment portion. Example:

Table A
ID Project Name Comment Comment Date
__________________________________________________ ________
1 Name 1 Comment 1.2 01/20/14
2 Name 2 Comment 2.2 02/14/14
3 Name 3 Comment 3.2 01/02/14

Obviously, I would use an Update query to override the previous information.

But let's say that I want to preserve the previous information for historical use? How would I set this up?