Strongly-guided 2D and 1D dielectric waveguides, which we call (dielectric) photonic wells and wires, can be used to modify the spontaneous emission properties of the active medium significantly. We will discuss how the photonic wells and wires can be used to realize efficient laser cavities. Semiconductor microcavity lasers based on photonic-well and photonic-wire structures will be described. They include the microdisk lasers, the photonic-wire lasers, and lasers with 1D photonic bandgap structures. We will discuss how with use of photonic-well or photonic-wire structures, the efficiency of capturing the spontaneous emission photons into a particular lasing mode (i.e. the spontaneous-emission coupling efficiency) can be as high as 10% to over 70%. The microdisk and photonic-wire laser realized will allow us to study spontaneous emission and lasing in low-dimensional photonic structures.