In the last twenty-five years, the existence of different ?states? in the X-ray emission of black-hole binaries and neutron-star Low-Mass X-ray Binaries (LMXBs) became evident. Very little work has been done on the third major type of X-ray binaries, namely High-Mass X-ray Binaries (HMXBs). In this talk I will present results from the first systematic study of four Be/XRBs during giant (type-II) outbursts. From color, spectral and timing properties, I will show how two different source states clearly emerge and two groups of systems can be defined.