A circumstellar disc (or circumstellar disk) is a torus-, pancake- or ring-shaped accretion disk of matter composed of gas, dust, planetesimals, asteroids, or collision fragments in orbit around a star. Around the youngest stars, they are the reservoirs of material out of which planets may form. Around mature stars, they indicate that planetesimal formation has taken place, and around white dwarfs, they indicate that planetary material survived the whole of stellar evolution. Such a disc can manifest itself in various ways.

According to the widely accepted model of star formation, sometimes referred to as the nebular hypothesis, a young star (protostar) is formed by the gravitational collapse of a pocket of matter within a giant molecular cloud. The infalling material possesses some amount of angular momentum, which results in the formation of a gaseous protoplanetary disc around the young, rotating star. The former is a rotating circumstellar disc of dense gas and dust that continues to feed the central star. It may contain a few percent of the mass of the central star, mainly in the form of gas which is itself mainly hydrogen. The main accretion phase lasts a few million years, with accretion rates typically between 10⁻⁷ and 10⁻⁹ solar masses per year (rates for typical systems presented in Hartmann et al.).

The disc gradually cools in what is known as the T Tauri star stage. Within this disc, the formation of small dust grains made of rocks and ices can occur, and these can coagulate into planetesimals. If the disc is sufficiently massive, the runaway accretions begin, resulting in the appearance of planetary embryos. The formation of planetary systems is thought to be a natural result of star formation. A Sun-like star usually takes around 100 million years to form.

The infall of gas onto a binary system allows the formation of circumstellar and circumbinary discs. The formation of such a disc will occur for any binary system in which infalling gas contains some degree of angular momentum. A general progression of disc formation is observed with increasing levels of angular momentum:

The indicative timescale that governs the short-term evolution of accretion onto binaries within circumbinary disks is the binary's orbital period ${\displaystyle P_{b}}$. Accretion into the inner cavity is not constant, and varies depending on ${\displaystyle e_{b}}$ and the behavior of the gas along the innermost region of the cavity. For non-eccentric binaries, accretion variability coincides with the Keplerian orbital period of the inner gas, which develops lumps corresponding to ${\displaystyle m=1}$ outer Lindblad resonances. This period is approximately five times the binary orbital period. For eccentric binaries, the period of accretion variability is the same as the binary orbital period due to each binary component scooping in matter from the circumbinary disk each time it reaches the apocenter of its orbit.

Eccentric binaries also see accretion variability over secular timescales hundreds of times the binary period. This corresponds to the apsidal precession rate of the inner edge of the cavity, which develops its own eccentricity ${\displaystyle e_{d}}$, along with a significant region of the inner circumbinary disk up to ${\displaystyle \sim 10a_{b}}$. This eccentricity may in turn affect the inner cavity accretion as well as dynamics further out in the disk, such as circumbinary planet formation and migration.

It was originally believed that all binaries located within circumbinary disk would evolve towards orbital decay due to the gravitational torque of the circumbinary disk, primarily from material at the innermost edge of the excised cavity. This decay is no longer guaranteed when accretion from the circumbinary disk onto the binary occurs, and can even lead to increased binary separations. The dynamics of orbital evolution depend on the binary's parameters, such as the mass ratio ${\displaystyle q_{b}}$ and eccentricity ${\displaystyle e_{b}}$, as well as the thermodynamics of the accreting gas.

Once a circumstellar disk has formed, spiral density waves are created within the circumstellar material via a differential torque due to the binary's gravity. The majority of these discs form axisymmetric to the binary plane, but it is possible for processes such as the Bardeen-Petterson effect, a misaligned dipole magnetic field and radiation pressure to produce a significant warp or tilt to an initially flat disk.