An arm joint is provided with a first coupling part with a first axis and a second coupling part with a second axis. Further, the arm joint includes a third coupling part connected in a manner rotatable around a third axis with the first coupling part. The third axis includes an angle with the first axis in the range of 30-60 degrees, preferably of 45 degrees. The third coupling part is connected in a manner rotatable around a fourth axis with the second coupling part. The fourth axis includes an angle with the second axis in the range of 30-60 degrees, preferably of 45 degrees. The third and the fourth axis mutually include an angle in the range of 60-120 degrees, preferably of 90 degrees. A robot arm with a number, preferably three, of such arm joints is also disclosed.