Haploidisation is the process of halving the chromosomal content of a cell, producing a haploid cell. Within the normal reproductive cycle, haploidisation is one of the major functional consequences of meiosis, the other being a process of chromosomal crossover that mingles the genetic content of the parental chromosomes.^[1] Usually, haploidisation creates a monoploid cell from a diploid progenitor, or it can involve halving of a polyploid cell, for example to make a diploid potato plant from a tetraploid lineage of potato plants.

If haploidisation is not followed by fertilisation, the result is a haploid lineage of cells. For example, experimental haploidisation may be used to recover a strain of haploid Dictyostelium from a diploid strain.^[2] It sometimes occurs naturally in plants when meiotically reduced cells (usually egg cells) develop by parthenogenesis.

Haploidisation was one of the procedures used by Japanese researchers to produce Kaguya, a mouse which had same-sex parents; two haploids were then combined to make the diploid mouse.

Haploidisation commitment is a checkpoint in meiosis which follows the successful completion of premeiotic DNA replication and recombination commitment.^[3]