  Context. We present the discovery of very high energy (VHE, E > 100GeV)
gamma-ray emission from the BL Lac object 1ES 1215+303 by the MAGIC telescopes
and simultaneous multi-wavelength data in a broad energy range from radio to
gamma-rays. Aims. We study the VHE gamma-ray emission from 1ES 1215+303 and its
relation to the emissions in other wavelengths. Methods. Triggered by an
optical outburst, MAGIC observed the source in January-February 2011 for 20.3
hrs. The target was monitored in the optical R-band by the KVA telescope that
also performed optical polarization measurements. We triggered target of
opportunity observations with the Swift satellite and obtained simultaneous and
quasi-simultaneous data from the Fermi Large Area Telescope and from the
Mets\"ahovi radio telescope. We also present the analysis of older MAGIC data
taken in 2010. Results. The MAGIC observations of 1ES 1215+303 carried out in
January-February 2011 resulted in the first detection of the source at VHE with
a statistical significance of 9.4 sigma. Simultaneously, the source was
observed in a high optical and X-ray state. In 2010 the source was observed in
a lower state in optical, X-ray, and VHE, while the GeV gamma-ray flux and the
radio flux were comparable in 2010 and 2011. The spectral energy distribution
obtained with the 2011 data can be modeled with a simple one zone SSC model,
but it requires extreme values for the Doppler factor or the electron energy
distribution.
