# What causes a magnetic field

Obviously, many would say, it is moving charge that causes a magnetic field. But then in my book all of the magnetic fields produced are assumed produced by stationary currents. That is currents that have been going on forever. Indeed my book actually states that you could write the Biot-Savart law for a point charge moving but it simply wouldn't be right. My question is then: What is the magnetic field of a point charge? Because surely it is a moving charge, so it must be producing a magnetic field. I am guessing this question is not so easy since my book has not touched upon the subject of magnetic fields from nonstationary currents, but surely they must be defineable?