This course serves as an introduction to the rapidly growing phenomena of light propagation at a reduced speed, commonly referred to as a "slow light". The course provides a basic understanding of the factors influencing the group velocity of light in dispersive media and in photonic structures. Important physical processes responsible for "slow light" are explained on a very accessible level. Potential practical applications of slow light are considered – tunable all-optical buffers and delay lines, low voltage electro-optic modulators, frequency converters and all-optical switches. For each application a set of metrics is introduced and various slow light schemes are compared on the basis of these metrics with an emphasis on the performance in high bit rate communication or signal processing systems. Practical methods for mitigation of high order dispersion and insertion loss are described.