In a recent game, my opponent started a kingside attack, and I, rather than passively defending, ignored his attack and started my own attack on the queenside. I eventually won the game.

In this situation, who had the initiative? Or did we both have it? Or did neither of us have it?

(This game is no longer in my game history, so I'm unable to show it.)

All things being equal, if your attack broke through first you must have had the initiative.

Frick. I just answered this question, but it didn't enter! Goh. Well, I'm not going to write it as brilliantly pellucid as before, but anyway...

So, initiative means, in its essence, for one side to be coercing the other side to react to their plans. It seems neither of you were reacting to each others plans, but rather were creating your own plans and ignoring your opponent's.

Therefore, as far as the initiative goes, neither of you had it, because neither of you were reacting to your opponent. Just because you won the game doesn't exactly mean you had the initiative, though (stating this in reference to previous poster).

But then, I'm not a prolific chess master, so I'm not omniscient in the field of positional play. Then again, I suppose no one who will ever read this question is.

That makes sense.  Thanks!

Yes, if you have the initiative the worst you can do is a draw.  Of course after an unsound sac if the initiative runs out you loose heh.