Welcome to Challenge h2g2, the place where you, the h2g2 Community, can alert your peers to gaps in the Edited Guide. So if you've noticed we have entries on every element of a topic except one, here's the place to tell everyone about it.

So get your thinking caps on and find the missing entries. It could well be that someone sees your suggestion and is inspired to plug that gap. Just start a conversation below starting with "Challenge:" and the the subject you think we need in the Guide.

And if someone nominates an entry that you'd like to work on, let them know here - it might well be that other Researchers will be only too willing to give you a hand.

• The Olympics - with the 2012 London Olympics looming on the horizon, we welcome Entries on all aspects of the Olympics. Tell us about an interesting incident in former games. Give us the low-down on an unusual sport such as Ice Dancing or Synchronised Swimming. Share with us your tips and tricks for your own favourite Olympic sport. We know that our Researchers are all super-fit, sporty types who are out breaking records when they're detached from their keyboards, so bring us the benefit of your experiences!

• Spain - our main entry on Spain was very old and not very complimentary to this fantastic country, so we've marked it as 'Mostly Harmless' and are inviting you to write something better. Lots of you go to Spain for your holidays every year, and some of even live there, so let's get writting...

• We've got lots about the Beatles, but we could really do with entries on other big bands from the 1960s whose influence can still be felt today - notably The Who.

• We'd love a complete set of British monarchs. You could start with mad King George III.

• The life of Jesus Christ - and how it's described differently in each Gospel.

• Filmmakers such as Steven Spielberg, George Lucas and Woody Allen.

• New Hampshire and Oklahoma are the only US States that don't have any entries to their name. Can you help?