Incompatible Changes since Mathematica Version 1

Every new version of the Wolfram Language contains many new features. But careful design from the outset has allowed nearly total compatibility to be maintained between all versions. As a result, almost any code written, say, for Mathematica Version 1 in 1988 should be able to run without change in Wolfram Language Version 13though it will often run considerably faster.
One inevitable problem, however, is that if code uses names that begin with uppercase letters, then it is possible that since the version when the program was first written, builtin functions may have been added to the Wolfram Language whose names conflict with those used in the program, or syntax changes and option specifications for that function may have changed, affecting its use.
In addition, to maintain the overall coherence of the Wolfram Language, some features that existed in earlier versions have gradually been droppedfirst becoming undocumented, and later generating warning messages if used. Furthermore, it has been necessary in some cases to make changes to particular functions that are not compatible with their earlier operation.
Between Versions 13 and 14

13.3 to 14.0

13.2 to 13.3

13.1 to 13.2

13.0 to 13.1

Between Versions 12 and 13

12.3 to 13.0

12.2 to 12.3

12.1 to 12.2

12.0 to 12.1

Between Versions 11 and 12

11.3 to 12.0

11.2 to 11.3

11.1 to 11.2

11.0 to 11.1

Between Versions 10 and 11
Between Versions 9 and 10
Between Versions 8 and 9
Between Versions 7 and 8
Between Versions 6 and 7
Between Versions 5 and 6
Between Versions 4 and 5
Between Versions 3 and 4
Between Versions 2 and 3
In the notebook front end, changes that were made include:
  • The file format for notebooks has been completely changed in order to support new notebook capabilities.
  • Notebook files are now by default given .nb rather than .ma extensions; .mb files are now superfluous.
  • The front end will automatically ask to convert any old notebook that you tell it to open.
  • The kernel command NotebookConvert can be used to convert notebook files from Version 2 to Version 3 format.
  • The default format type for input cells is now StandardForm rather than InputForm.
  • The organization of stylesheets, as well as the settings for some default styles, have been changed.
  • Some command key equivalents for menu items have been rearranged.
  • Between Versions 1 and 2