An unexpected characteristic of low surface brightness galaxies ( LSBGs ) is that a significant number are massive and possess substantial amounts of atomic gas .
We present preliminary results of an ongoing program to obtain BVRIJHK imaging , along with some nuclear spectroscopy , of a well-defined sample of LSBGs which are gas-rich and of similar size to giant , high surface brightness spiral galaxies ( HSBGs ) .
These LSBGs span the entire range of Hubble disk morphologies .
While their disks are bluer , on average , than comparable HSBGs , the optical morphology of massive LSBGs indicates that many of these systems have undergone previous star formation episodes .
They typically have long disk scale lengths , and range from M _ { B } = -16 to -22 ( H _ { 0 } = 75 km s ^ { -1 } Mpc ^ { -1 } ) .
About half of the LSBGs with bulges show evidence of nuclear activity , and \sim 30 % have appear to be barred .
These massive , gas-rich LSBGs apparently have varied , and often complex , evolutionary histories .