Intersubband transitions in GaAs/(Al,Ga)As quantum wells have been successfully used in the design of novel infrared detectors for over a decade now. Both conduction- and valence-band based detectors have been investigated. In general, the conduction-band based detectors fabricated from direct gap GaAs/(Al,Ga)As heterostructures are not sensitive to normal-incidence light. This is a consequence of the quantum mechanical rules that govern light absorption in these structures. In order to detect normal-incidence light, a grating structure which scatters the incident light into higher order, transverse magnetic modes is used. To avoid the use of gratings, research is being carried out in (In,Ga,Al)As/(Al,Ga)As conduction-band quantum well structures that can absorb normal-incidence light. This paper reviews recent progress in such detectors.