Genome size in plants is characterised by its extraordinary range. Although it appears that the majority of plants have small genomes, in several lineages genome size has reached giant proportions. The recent advent of next-generation sequencing (NGS) methods has for the first time made detailed analysis of even the largest of plant genomes a possibility. In this review, we highlight investigations that have utilised NGS for the study of plants with large genomes, as well as describing ongoing work that aims to harness the power of these technologies to gain insights into their evolution. In addition, we emphasise some areas of research where the use of NGS has the potential to generate significant advances in our current understanding of how plant genomes evolve. Finally, we discuss some of the future developments in sequencing technology that may further improve our ability to explore the content and evolutionary dynamics of the very largest genomes.