Nanopores are nanometer-sized pores or holes formed in biological or synthetic materials, through which individual molecules can pass. These pores are typically embedded in thin membranes and serve as single-molecule sensors. In molecular sequencing, nanopores are used to sequence and deoxyribonucleic acid (DNA), ribonucleic acid (RNA), or even proteins. In the context of DNA sequencing, it produces a unique change in the ionic current, which can be detected and interpreted to determine the sequence of the DNA strand. This chapter outlines the principles of nanopore sequencing, types of nanopores, sequencing for DNA and RNA along with their applications. This chapter also addresses nanopores sequencing platforms, along with the challenges and limitations of nanopores in signal noise and error rates. The division winds up with future prospects and emerging frontiers in nanopores technology.