In this introduction, I show that Silvan Tomkins’s affect system is an effective critical apparatus for evaluating literary modernism’s unique handling of character. Well acquainted with the physical sciences, Tomkins instills foundational thermodynamic concepts into his theories, revealing that affect behaves entropically. Tomkins encourages us to envision the conscious self as consonant not only with the coterminous internal subsystems with which the self overlaps and intermingles, but also with the external systems that house the self. Such a model allows for fresh examinations of modernism’s situation and formation of character within entropic settings. Modernism’s sharp focus on the individual, in turn, underscores that meaning is made, not in isolation, but by virtue of connections formed within a network of systems. The individual, therefore, becomes a case study for experiences that are widely applicable. Affect theory provides the lexicon for these robust new analyses of character within the intricate networks exemplified in modernist literature.