What is the difference between Shonen and Seinen?

[Guernsey]

I have admit before I came to this site I would not have known the difference between the two genres but I know a little bit about shonen and seinen. I mostly watch some shonen in the Spring/Summer season because that is time where I feel a little "happy" and I am not as depressed but in the Autumn/Winter I tend to watch more Seinen where I want to learn more about character relationships as opposed to action. I believe this seasonal depression but that is not the point of thread, the thing I want to ask is what is the real difference between anime such as Bleach or Toradora? I don't watch that many anime nowadays due to my short attention span and I may not keep up with the latest titles but I do manage to watch something interesting. While I see some similairities, I do note some differences but I am not really all that aware of a lot of it, does anyone here have concrete knowledge on the topic? Can psychological anime have shonen type action or can shonen be as serious as seinen?

[yezhanquan]

In practical terms, seinen manga rarely has the tiny hiragana written alongside kanji to help readers. Shounen manga usually has that.

Generally, seinen series tend to be somewhat darker and more "realistic" than shounen series. Also, they dabble more in words than action. Sure, Hellsing is packed to the brim in action, but its dialogue contains much food for thought as well.

[Jan-Poo]

the only difference is the targeted population. Shounen are aimed to teenagers Seinen are aimed to young adults and adults.

The "little kanji" yezhanquan is talking about are called "furigana" and they are used to help in the reading of complex Kanji. The reason you don't find them in Seinen it's because the targeted population of Seinen is supposed to already know how to read them, while a part of the "shounen" population is still in the process of learning.

[Kimura sensei]

Originally Posted by Jan-Poo

the only difference is the targeted population. Shounen are aimed to teenagers Seinen are aimed to young adults and adults.

That's it.

Shonen: for young boys
Shoujo: for young girls
Seinen: for adult men
Josei: for adult women

A few comments:
Moe series usually are seinen.
Some shonen series have a really big female following (see how many yaoi fangirls of Naruto are out there).
And some shoujo series are liked by adult men (Shugo Chara and Precure, for example)