Interpretation of acoustic emission (AE) signals in terms of damage mechanisms in composite materials and structures is often difficult. This is because of the multitude of damage mechanisms. In the present study, glass fiber/epoxy (GF/EP) (0m/90n)s cross-ply laminates were studied in unixial tensile loading. Since the damage mechanisms in such laminates are primarily matrix cracking, acoustic emission interpretation was facilitated. Real-time optical microscopy and AE studies were conducted in order to identify details of the damage development. It was found that a multitude of secondary cracking events occurred at higher strains. These events may explain why stress analysis models based on straight and regularly spaced transverse cracks are not successful. In addition, it was clearly demonstrated that in order to interpret damage development with some confidence from AE-data, direct observations of damage events must also be performed.