We will introduce the field of large-scale programmable photonics. In the past few years, new concepts for general-purpose, programmable photonic integrated circuits (PIC) have been proposed to manipulate light in a more flexible way. Today, most PICs are developed for one function, and are therefore called application-specific photonic integrated circuits (ASPIC), and a new chip has to be designed for each new application The new class of programmable PICs can be used more like electronic microcontrollers and field-programmable gate arrays (FPGA), and programmed in software for different tasks. Simple programmable PICs have already been experimentally demonstrated, reproducing functionality in programming hitherto limited to custom-designed hardware. This programming is done through electro-optic tuners like waveguide heaters or MEMS. We will discuss different architectures for programmable PICs, and the technology stack that is needed to realize the full programmable PICs: waveguides, actuators, monitors, control loops, programming algorithms and a user interface that makes the hardware accessible to the users. We will briefly discuss the economics behind programmable PICs, and draw parallels with programmable electronics, which have put complex functionality in the hands of the maker community.