A Tumblr network is a group of blogs that come together to socialize, discuss a particular topic or a range of topics, promote each other, get HTML help, etc. Some networks accept blogs that focus on a particular topic and some do not. To join a Tumblr network, you’d simple search the Tumblr Networks tag or the Networks tag on Tumblr. Pick which one you’re interested in and read the instructions on how to join. It’s a good way to make new friends on Tumblr who share your interests.