From Kodansha Comics:
Humanity has been devastated by the bizarre, giant humanoids known as the Titans. Little is known about where they came from or why they are bent on consuming humanity. Seemingly unintelligent, they have roamed the world killing off humankind for years. For the past century, what's left of mankind has hidden in a giant, three-walled city. People believe their 100-meter-high walls will protect them from the Titans, which are 10 to 20 meters tall. But the sudden appearance of an immense Titan is about to change everything.
Attack on Titan is a breakout hit in Japan, where the first five volumes of the series have sold over 5.5 million copies in just 18 months. The series has won multiple manga awards, including Best Shonen Manga of 2010.