  We present the basic concept of a new astronomical instrument: SPARC4 -
Simultaneous Polarimeter and Rapid Camera in 4 bands. SPARC4 combines in one
instrument: (i) photometric and polarimetric modes; (ii) sub-second
time-resolution in photometric mode and excellent time-resolution in
polarimetric mode; (iii) simultaneous imaging in four broad-bands for both
modes. This combination will make SPARC4 a unique facility for ground-based
optical observatories. Presently, the project is in its conceptual design
phase.

Instrumentation and Methods for Astrophysics