1. To decide to do something even though it was not one's responsibility. Typically followed by "to do something." I took it upon myself to print out some informational packets for the meeting since I knew it might be confusing for some people. We don't have enough time to cover all of this in class, so you'll need to take it upon yourselves if you want to learn more.

2. To bear some burden, difficulty, or responsibility on one's own or for oneself. I feel like Tom is taking too many financial responsibilities upon himself. You really shouldn't take other people's emotional baggage upon yourself. It can be really damaging if you're not careful.