Currently there is no Federal law which says that Internet Gambling is
illegal. That is Federal. States however are a mess. Washington State
for example just made it a Felony (upgrading it from a misdemeanor).
This website has a table for each state and the infraction that is attached:
State Gambling Law Summary for All US States
I didn't notice any state where it wasn't currently a misdemeanor or a
felony. The notes at the bottom however are somewhat amusing. For
example, in North Dakota it is only seen as illegal if the hand is
worth more than $25, or your are wagering more than $25 in the game.
However, it is not a misdemeanor until the amount reaches $500.
It is illegal, currently (again, this is being debated and may change
soon as well) to pay for gambling online with a credit card.
The articles below may help clarify these things, or may just confuse
you more, as we all are a bit confused. What is clear, is that
currently there is not Federal Law against it, but every State has
some type of legislation against online poker and you would be wise to
learn and understand what those laws are, and keep up-to-date with
them as well.
Articles of Interest
Online Poker Legal?
Online Gambling Laws
Laws.com: Leading Journal of Internet Laws
Articles and Notes on Gambling Laws United States, Stats, Federal
All of this could change very soon ...
Federal Legislation moving through Congress