LDPC codes are one of the current topics in information coding theory these days. Invented in the early 1960s, these codes have experienced impressive comeback in the almost last twenty years. These codes are similar to other linear block codes except the sparse parity check matrix and the decoding algorithms. These are giving good performance in the presence of noise. The purpose of writing this review paper is to summarize the study about these codes. This paper would sum up coding and decoding techniques of these codes along with various strategies of code design. LDPC codes are not only attractive from a theoretical point of view, but also perfect for practical applications in the field.