Does green tea have caffeine? In short, yes. But the important question is: How much? That’s a much harder question, because different studies have found that the caffeine content of any given cup of green tea varies.
If you were to rely entirely on Yahoo! Answers for your answer to whether green tea contains caffeine, you’d find yourself very confused indeed. Take this page, for example. First answer: “No it doesn’t.” Second and third answer: “Yes it does”.
The truth is, green tea does contain caffeine. But if people will try to tell you that a cup of green tea contains X amount of caffeine, take it with a grain of salt. The caffeine level of any given cup of tea you drink varies based on how long you allow your tea to brew, how hot the water is and whether it’s the second (or subsequent) brewing of the same batch of tea leaves. There are also variations of caffeine content based on how the tea is produced. (For more on the factors affecting tea’s caffeine content, I can recommend The Story of Tea: A Cultural History and Drinking Guide by Mary Lou Heiss and Robert J. Heiss.)
Given these variations, it’s impossible for most of us to know how much caffeine our tea contains. One average figure I’ve seen is that green tea contains about 20 mg of caffeine. This is half of what black tea contains and about a quarter the caffeine content of your average cup of coffee. But as I said, these are averages, and there is significant deviation from the mean.