In this chapter, we have described the JPEG standard for still image compression. We discussed the details of the algorithm for lossless JPEG. We have also discussed in great detail the principles and algorithms for the baseline JPEG standard. Baseline JPEG is the most used and popular algorithm amongst all different modes in JPEG standard for still image compression. We have presented some results of baseline JPEG and compared with the new JPEG2000 standard. The features, concepts, and principles behind the algorithms for JPEG2000 standard will be elaborated in great detail in Chapters 6, 7, 8 and 10. We also summarized the progressive mode and hierarchical mode of operation of the JPEG standard in this chapter with examples.