We live in an era of ever larger and deeper sky surveys, covering a broad range of wavelengths. A number of surveys are ongoing (e.g., VISTA, VST, Pan-STARRS), others are on the verge of being started/launched (e.g., DES, SkyMapper, Gaia, eROSITA, ASKAP), while yet others have been approved for construction (e.g., Euclid, LSST, SKA). To reach their full potential and their most ambitious science goals, all these surveys are in strong need of large-area, high-multiplex spectroscopic follow-up in order to identify and characterize detected sources. While current facilities are used to conduct large spectroscopic surveys (e.g., RAVE, Gaia-ESO, Sloan/SEGUE/BOSS/APOGEE), the new flood of imaging surveys will require a next generation of spectroscopic survey instruments.
The 4MOST facility aims to be such a next generation of survey facility for the ESO community, starting observations early 2019. With ~2400 fibres in a 5 square degree field-of-view on the 4m-class VISTA telescope and with spectrographs of resolution R~5000 and R~20,000 covering most of the optical wavelength range, 4MOST is foreseen to cover in a 5-year survey most of the Southern sky 2-3 times resulting in ~20 million spectra. 4MOST will run a number of large, general-purpose Public Key Surveys of Galactic and extra-galactic nature directed by the 4MOST consortium, producing higher-level data products to the whole community. In addition, 4MOST will be able to perform other 5-year programs which will be incorporated into the observing program after a normal peer review process, either in parallel with the Public Key Surveys using a fraction of the fibres or as dedicated surveys in regions of particular interest. By presenting 4MOST’s planned survey capabilities and by reviewing the needs of the whole community we want to make sure that the 4MOST instrument requirements and envisioned survey strategies will enable the broadest range of science and that best possible synergies with other projects are reached.