Invariant representation learning is a machine learning approach that transforms input data into an internal feature space designed to retain information necessary for predicting a target outcome while remaining invariant to or independent of specific extraneous factors, protected attributes, or domain shifts. By intentionally neutralizing task-irrelevant or sensitive variations, this technique enables models to achieve a balance between predictive accuracy and invariance constraints. It is widely applied across diverse subfields, including algorithmic fairness to eliminate bias against demographic groups, privacy-preserving machine learning to remove sensitive identity markers, and domain generalization to ensure consistent and reliable performance across varying environments.