Linked from
The 27 pages that link to Sigma-algebra, each with the reason it gives.
Lebesgue measureNarrower topic: Lebesgue measure is defined on a sigma-algebra of subsets.
Power setBroader topic: It selects measurable collections from the full power set of a space.
Measure theoryRelated: It specifies which sets a measure is allowed to assign sizes.
Probability spaceRelated: It determines which subsets of outcomes qualify as events.
Event (probability theory)Related: Only subsets in this collection are measurable events.
Measure spaceRelated: It specifies exactly which subsets can receive a measure.
Radon–Nikodym theoremRelated: Measures and measurable densities are defined relative to σ-algebras.
Tonelli's theoremRelated: It specifies which subsets in each factor space are measurable.
Probability axiomsRelated: Probability is defined only for events in the model's sigma-algebra.
Hahn decomposition theoremRelated: Both pieces of the decomposition must be measurable.