Genome size varies c. 2400-fold in angiosperms (flowering plants), although the range of genome size is skewed towards small genomes, with a mean genome size of 1C. =. 5.7. Gb. One of the most crucial factors governing genome size in angiosperms is the relative amount and activity of repetitive elements. Recently, there have been new insights into how these repeats, previously discarded as 'junk' DNA, can have a significant impact on gene space (i.e. the part of the genome comprising all the genes and gene-related DNA). Here we review these new findings and explore in what ways genome size itself plays a role in influencing how repeats impact genome dynamics and gene space, including gene expression.