World’s most important/most pressing challenges

My most important challenge is getting up in a morning when the alarm goes off, rather than switching the alarm off and going back to sleep. After that it's making sure I get my first cup of tea.

I agree with KiloNova and Mandolinear; the biggest problem is the environment - too many people eating away at all the resources.

Now, there is another level to this problem. It's difficult to get everyone into action to protect the environment, and one of the reasons is that some of the world leaders are the wrong people for that job. So, the challenge becomes: how to organise people to vote for green parties, join environmental pressure groups, etc.

Of course, some countries do not have a democratic process like that.