  [Abridged] The Sardinia Radio Telescope (SRT) is the new 64-m dish operated
by INAF (Italy). Its active surface will allow us to observe at frequencies of
up to 116 GHz. At the moment, three receivers, one per focal position, have
been installed and tested. The SRT was officially opened in October 2013, upon
completion of its technical commissioning phase. In this paper, we provide an
overview of the main science drivers for the SRT, describe the main outcomes
from the scientific commissioning of the telescope, and discuss a set of
observations demonstrating the SRT's scientific capabilities. One of the main
objectives of scientific commissioning was the identification of deficiencies
in the instrumentation and/or in the telescope sub-systems for further
optimization. As a result, the overall telescope performance has been
significantly improved. As part of the scientific commissioning activities,
different observing modes were tested and validated, and first astronomical
observations were carried out to demonstrate the science capabilities of the
SRT. In addition, we developed astronomer-oriented software tools, to support
future observers on-site. The astronomical validation activities were
prioritized based on technical readiness and scientific impact. The highest
priority was to make the SRT available for joint observations as part of
European networks. As a result, the SRT started to participate (in shared-risk
mode) in EVN (European VLBI Network) and LEAP (Large European Array for
Pulsars) observing sessions in early 2014. The validation of single-dish
operations for the suite of SRT first light receivers and backends continued in
the following years, and was concluded with the first call for
shared-risk/early-science observations issued at the end of 2015.
