A cellular bleb grows when a portion of the cell membrane detaches from the
underlying cortex under the influence of a cytoplasmic pressure. We develop a quantitative model
for the growth and dynamics of these objects in a simple two-dimensional setting. In particular,
we first find the minimum cytoplasmic pressure and minimum unsupported membrane length for
a stationary bleb to nucleate and grow as a function of the membrane-cortex adhesion. We next
show how a bleb may travel around the periphery of the cell when the cytoplasmic pressure varies
in space and time in a prescribed way and find that the traveling speed is governed by the speed
of the pressure change induced by local cortical contraction while the shape of the traveling bleb
is governed by the speed of cortical healing. Finally, we relax the assumption that the pressure
change is prescribed and couple it hydrodynamically to the cortical contraction and membrane
deformation. By quantifying the phase space of bleb formation and dynamics, our framework
serves to delineate the range and scope of bleb-associated cell motility.