  We review our current understanding to the accretion and ejection processes
in Sgr A*. Roughly speaking, they correspond to the quiescent and flare states
of the source respectively. The high-resolution {\it Chandra} observations to
the gas at the Bondi radius combined with the Bondi accretion theory, the
spectral energy distribution from radio to X-ray, and the radio polarization
provide us strict constraints and abundant information to the theory of
accretion. We review these observational results and describe how the
advection-dominated accretion flow model explains these observations. Recently
more attentions have been paid to flares in Sgr A*. Many simultaneous
multi-wavelength campaigns have been conducted, aiming at uncovering the nature
of flares. The main observational properties of flares are briefly reviewed.
Especially, the time lag between the peaks of flare at two radio frequencies
strongly indicates that the flare is associated with ejection of radio-emitting
blobs from the underlying accretion flow. Such kind of episodic jets is
distinctive from the continuous jets and are quite common in black hole
systems. We introduce the magnetohydrodynamical model for the formation of
episodic jets recently proposed based on the analogy with the theory of coronal
mass ejection in the Sun. We point out that the various observational
appearances of flares should be explained in the framework of this model, since
ejection and flare originate from the same physical process.
