Pulsar timing array (PTA) uses ultra-stable millisecond pulsars to detect gravitational waves (GWs) in the nano-Hz frequency band. The PTA experiments monitor and measure arrival times of pulses. There are several physical processes which cause deviations from the expected arrival times of these radio pulses among which (the most relevant to us) are GWs. The most promising sources in the PTA are super-massive  black hole binaries (SMBHBs) that form through the mergers of massive galaxies. Inspiralling SMBHBs produce a stochastic GW background (GWB) and/or individual periodic signals.  In this presentation I will overview of current activities in PTAs with the focus on European Pulsar Timing Array. I will present the latest results reporting detection of the common red noise signal by NanoGrav, PPTA and EPTA and discuss its possible interpretation.