How Much Caffeine Is There In Tea?

The caffeine content of tea depends both on what type of tea you are making, and on how you brew / prepare the tea.  The caffeine content varies widely from one tea to the next.  It generally varies from 15mg to 75mg per 8oz cup, with typical teas being around 40mg, but it can be lower or higher if you brew it more strongly.  This is a lot less than a cup of coffee, which typically contains 80-135mg in the same sized cup.

Using more tea leaf, and steeping for longer times results in more caffeine.

It's not possible to generalize about green tea, white tea, black tea, or any broad class of teas containing more or less caffeine.  For example, it is a myth that white tea is lowest in caffeine.  This is not true.  White teas, like any kind of tea, can be low, high, or intermediate in caffeine.  Flavored teas can be lower in caffeine if the tea plant is blended with other ingredients that take up space and impart flavor but do not contain any caffeine.

The caffeine content of the loose-leaf tea is mainly a function of what part of the plant is used.  The tips or leaf buds contain the most caffeine, and the mature leaves and stems the least, so "tippy" teas (like Yunnan gold or tippy Assam, used in some Irish Breakfast blends), and teas made exclusively from buds (like Silver needle white tea) are highest in caffeine.  Teas made from large, mature leaves (like Lapsang Souchong, or Shou Mei white tea) or from stems (Kukicha), tend to be lowest in caffeine.

You can read more about why this is the case, and read about particular varieties that are high or low in caffeine, on this page about caffeine in tea.

Tea is one of the most popular beverages in the world standing second only to water. There are actually four types of tea: green tea, black tea, white tea and oolong tea. The caffeine content in tea is generally about 3 percent, which is 40mg in every cup of tea prepared.
Tea is also a natural source of caffeine and it does not contain any amount of proteins or carbohydrates.
The tea that is found in tea-bags is all blended. In fact most of the other teas which are sold over the entire United Kingdom are blended.
Tea is also one of the most favorite beverages at an afternoon party; some cultures also include tea ceremonies (for example the famous Korean tea ceremony).

Tea is, as coffee, another common source of caffeine. Actually, tea has more caffeine than coffee, but as we use more water in a tea, it is not that strong...and does not have the same effect on our body.
I actually prefer English tea for breakfast.

Here is a very useful table of caffeine content:
coffeetea.about.com

And here, all you need to know about caffeine:
en.wikipedia.org