Note: This bento safety article is one of the first ones I posted here on Just Bento, back in November 2007. I've edited it and added some more information, especially since more and more new people are coming to the site. Even if you're a veteran bento maker, it's good to go over the basics occasionally!
A traditional portable bento box meal is meant to be eaten eaten at room temperature. It's typically made in the morning, then held for a few hours until lunchtime, also at room temperature. Millions and millions of Japanese people eat bentos like this (as well as an increasing number of people all around the world). There are some basic, time-tested precautions to take to ensure that your bento box meals will be tasty and safe when you tuck into them.