Massive stars inject energy into the surrounding 
medium and form shell structures. Bubbles are blown by 
fast stellar winds from individual massive stars, while 
superbubbles are blown by fast stellar winds and 
supernova explosions from groups
of massive stars. Bubbles and superbubbles share a 
similar overall structure: a swept-up dense shell with an 
interior filled by low-density hot gas. Physical properties 
of a bubble/superbubble can be affected by magnetic 
field, thermal conduction, turbulent mixing, 
inhomogeneous ambient medium, etc.
I will review recent progresses on observations and 
compare them to theoretical expectations for (1) swept-
up dense shells, (2) hot interiors, and (3) interface 
between a dense shell and
its interior hot gas.