This MIT course, 6.451 Principles of Digital Communication II, has 25 video lectures by Professor David Forney from Massachusetts Institute of Technology. The course is the second part of a two-course sequence on digital communication. The first course is 6.450 Principles of Digital Communications I. Some of the topics included on these video lectures are trellis representations of binary linear block codes and trellis-based decoding; codes on graphs; the sum-product and min-sum algorithms; the BCJR algorithm; turbo codes, LDPC codes and RA codes; and performance of LDPC codes with iterative decoding. Finally, the course addresses coding for the bandwidth-limited regime, including lattice codes, trellis-coded modulation, multilevel coding, shaping and linear Gaussian channels.This course is the second of a two-term sequence with 6.450. The focus of these video lectures is on coding techniques for approaching the Shannon limit of additive white Gaussian noise (AWGN) channels, their performance analysis, and design principles. After a review of 6.450 and the Shannon limit for AWGN channels, the course begins by discussing small signal constellations, performance analysis and coding gain, and hard-decision and soft-decision decoding. It continues with video lectures on binary linear block codes, Reed-Muller codes, finite fields, Reed-Solomon and BCH codes, binary linear convolutional codes, and the Viterbi algorithm.