  One of the most exciting discoveries of recent years is a pair of gigantic
gamma-ray emission regions, the so-called Fermi bubbles, above and below the
Galactic center. The bubbles, discovered by the Fermi space telescope, extend
up to $\sim 50^\circ$ in Galactic latitude and are $\sim 40^\circ$ wide in
Galactic longitude. The gamma-ray emission is also found to correlate with
radio, microwave and X-rays emission. The origin of the bubbles and the
associated non-thermal emissions are still not clearly understood. Possible
explanations for the non-thermal emission include cosmic-ray injection from the
Galactic center by high speed Galactic winds/jets, acceleration by multiple
shocks or plasma turbulence present inside the bubbles, and acceleration by
strong shock waves associated with the expansion of the bubbles. In this paper,
I will discuss the possibility that the gamma-ray emission is produced by the
injection of Galactic cosmic-rays mainly protons during their diffusive
propagation through the Galaxy. The protons interact with the bubble plasma
producing $\pi^\circ$-decay gamma rays, while at the same time, radio and
microwave synchrotron emissions are produced by the secondary
electrons/positrons resulting from the $\pi^{\pm}$ decays.
