panel-data

I have several data frames in panel data form. Now I want to merge these panel data frames into one panel data. These data frames have common and different between them. I illustrate as follows: df1: Month variable Beta1 Beta2 Beta3 Beta4 Beta5 Beta6 Jan-05 A 1 2 3 4 5 6 Feb-05 A 2 3 4 5 6 7 Mar-05 A 3 4 5 6 7 8 Apr-05 A 4 5 6 7 8 9 May-05 A 5 6 7 8 9 10 Jun-05 A 6 7 8 9 10 11 Jul-05 A 7 8 9 10 11 12 Aug-05 A 8 9 10 11 12 13 Sep-05 A 9 10 11 12 13 14 Oct-05 A 10 11 12 13 14 15 Nov-05 A 11 12 13 14 15 16 Dec-05 A 12 13 14 15 16 17 Jan-05 B 12 12 12 12 12 12 Feb-05 B 12 12 12 12 12 12 Mar-05 B