EMMA (Experiment with Multi-Muon Array) is an underground detector array designed for cosmic-ray composition studies around the knee energy (or ∼ 1 − 10 PeV). It operates at the shallow depth in the Pyh¨asalmi mine, Finland. The array consists of eleven independent detector stations ∼ 15 m2 each. Currently seven stations are connected to the DAQ and the rest will be connected within the next few months. EMMA will determine the multiplicity, the lateral density distribution and the arrival direction of high-energy muons event by event. The preliminary estimates concerning its performance together with an example of measured muon multiplicities are presented.