Though I find the TIOBE index interesting, the error margins are huge. The top 5 seem fairly accurate. Considering the error margins, you'll notice there's a m

Though I find the TIOBE index interesting, the error margins are huge. The top 5 seem fairly accurate. Considering the error margins, you'll notice there's a massive drop-off after position 5. (#1 - 21%, #5 - 9% and #6 - 5%). You can safely forget about accuracy after that. I am a little surprised at C#'s low rating. JavaScript's position seem reasonable - not everyone is building web apps. I do a ton of JS development myself and we're using it to squeeze every last drop out of the browser. Recruitment efforts on our end for this tend to focus on keywords like C, Haskell, LISP, assembly. Most JS positions in the market are for DOM manipulation and AJAX responses. I keep my CV up-to-date, but don't emphasize the JS aspect. The 10:1 ratio of JS to ActionScript seems a little off, but I guess that's because most job ads look for 'Flash Developer' as opposed to 'ActionScript Developer'. Delphi is up? Uh, what? And PowerShell is in the top 20 - higher than bash/csh/ksh and even higher than Lua? (I know a lot of game developers - Lua is fairly big in that sector). Don't take lists like this as a guideline for your personal development. They're an indication of the current state and an error-prone one at that. That said... I think you should all be reasonably comfortable with C, Java, C# and two of Ruby, Python or Perl. And then throw in one or more of OCaml, Scheme, LISP, Haskell, what have you. Oh, and assembly of course. Pick an architecture but get down and dirty with the a malloc implementation or two. In closing, language popularity doesn't mean much.