A field campaign was conducted in Greece during the summer of 2012 (June 8 – July 26) to investigate ambient particulate matter (PM) levels, chemical composition and contribution of regional and local sources. Simultaneous collection of PM1, PM2.5 and PM10 samples took place in seven different sampling sites in Greece. The sampling sites included: i) one urban and one suburban station in Patras, ii) one suburban in Thessaloniki, iii) one suburban and one background station in Athens, iv) one rural background station at the Navarino Environmental Observatory (NEO) in southwest Peloponnese and v) one remote background site at Finokalia in the northeast part of Crete. These different sites were chosen in order to estimate the contributions of the local emissions sources and long range transport. A suite of continuous/online instruments was deployed in selected sites including an Aerodyne High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF AMS), an Aerosol Chemical Speciation Monitor (ACSM), a Proton-Transfer Reaction Mass Spectrometer (PTR-MS), a PM2.5/PM10 Tapered Element Oscillating Microbalance (TEOM), filter samplers (PM1, PM2.5 and PM10), nephelometers, aethalometers and gas-phase monitors. The campaign PM2.5 average ranged from 14 to 20 μg m-3 for the different sites. The fine PM mass concentration and chemical measurements were quite similar in all sites suggesting significant contributions of transported regional pollution and smaller contributions of local sources. Sulfate and organics were major PM2.5 components in all sites. Also nitrate, dust and sea-salt for the coastal areas were also important components of the PM10 fraction. The sulfate levels were similar in all sites, while the concentration of the organics and dust were more variable. Most of the organic aerosol was highly oxygenated. Back trajectory analysis, based on FLEXPART, identified five source regions (Greece, Athens, Turkey, Balkans, marine) each of which influenced the PM1 aerosol composition. / --