Single photon counting (SPC) and time correlated single photon counting (TCSPC) techniques have been developed in the past four decades relying on photomultiplier tubes (PMT), but interesting alternatives are nowadays provided by solid-state single photon detectors. In particular, silicon Single Photon Avalanche Diodes (SPAD) fabricated in planar technology join the typical advantages of microelectronic devices (small size, ruggedness, low operating voltage and low power dissipation, etc.) with remarkable basic performance, such as high photon detection efficiency over a broad spectral range up to 1 mum wavelength, low dark count rate and photon timing jitter of a few tens of picoseconds. In recent years detector modules employing planar SPAD devices with diameter up to 50 µm have become commercially available. SPADs with larger active areas would greatly simplify the design of optical coupling systems, thus making these devices more competitive in a broader range of applications. By exploiting an improved SPAD technology, we have fabricated planar devices with diameter of 200 mum having low dark count rate (1500 c/s typical @ -25 °C). A photon timing jitter of 35 ps FWHM is obtained at room temperature by using a special pulse pick-up network for processing the avalanche current. The state-of-the-art of large-area SPADs will be reviewed and prospects of further progress will be discussed pointing out the challenging issues that must be faced in the design and technology of SPAD devices and associated quenching and timing circuits.