Petrus (Piet) Groeneboom (born 24 September 1941[2] in Scheveningen[3]) is a Dutch statistician who made major advances in the field of shape-constrained statistical inference such as isotonic regression, and also worked in probability theory.

Following his retirement he came to public attention for his statistical work in the retrial of Lucia de Berk, a Dutch nurse, who had been convicted of murder.

In 1979, Groeneboom, together with Kobus Oosterhoff and Frits H. Ruymgaart, formulated and proved Sanov's theorem in a finer topology than had been known at the time.

[5] A paper he published in 1983 on properties of Brownian motion gave rise to a large body of literature on minorants of more general stochastic processes.

The iterative convex minorant algorithm which he introduced in 1991 found use in statistical estimation for proportional hazards models.

[13] Together with Eric Cator, Groeneboom contributed to the probabilistic analysis of the Hammersley process, a continuous interacting particle system (IPS).

[15] They argued that statistical considerations that had led to the initial suspicions of murder, and those which had remained at the center stage of the case afterwards, were flawed.