Photonic integrated circuits (PICs) combine hundreds of optical components on a chip, and can enable fast communications, high-performance computing, and improved sensing. PICs, made by miniaturized optical waveguides, require many reconfigurable elements to enable programmable functionalities and to compensate for fabrication variations and environmental factors. However, current reconfiguration methods consume large amounts of electrical power, which is a bottleneck for their scalability, and limits their applications. A promising technology to alleviate this bottleneck is photonic microelectromechanical systems (MEMS), which provides low-power reconfiguration of PICs using electromechanical actuation. This thesis reports on several photonic MEMS devices and technologies that enable low-power reconfiguration for PICs, and bring new functionalities towards efficient nonlinear optics, optical beam steering, and photonic Lab-on-chips (LoCs). A fundamental element of reconfigurable PICs is the phase shifter, and this thesis introduces novel photonic MEMS phase shifters with low power consumption, low optical losses, and linear actuation, and applies them to reconfigurable filtering. Moreover, photonic MEMS bring novel functionalities arising from the mechanical movement of waveguide components, and, in this thesis, a method to tune waveguide dispersion for efficient nonlinear optics in silicon, and two types of reconfigurable waveguide gratings for low-power optical beam steering are developed. The photonic MEMS platform introduced in this thesis can be combined with polarization diversity schemes by using a novel suspended polarization beam splitter. In addition, other technologies addressing challenges in integrated photonics are introduced, such as a lithium niobate on insulator (LNOI) platform that combines grating couplers, high confinement waveguides, and Bragg gratings, for electro-optic modulation and efficient nonlinear optics; and a cost-efficient method to integrate photonic sensors into LoCs for healthcare applications. The technologies introduced in this thesis have potential to enable large-scale, power-efficient, and highly functional PICs, with prospects for more efficient and more functional optical information technologies.