For a large fraction of its already twenty year long existence, the COMPASS collaboration has
studied the polarised structure of the nucleon via muon-nucleon scattering. This paper summa-
rizes the final results obtained in longitudinally polarised DIS, either inclusive or semi-inclusive.
For inclusive DIS, these cover the measurements of structure function g1 , and the information ex-
tracted from them in terms of polarised PDFs (pPDFs) and Bjorken sum rule. From g1 measure-
ments alone, combining COMPASS with world data, the quark spin contribution to the nucleon
spin is determined to be 0.26 < ∆Σ < 0.36. And from COMPASS data alone, the Bjorken sum
rule is verified to 9% accuracy. In semi-inclusive DIS, more information can be gained on the
pPDFs of sea quarks and gluons. A selection of our achievements along this line are reported.