Purpose of review: Neurobiological research literature on anxiety and anxiety disorders of the previous year (April 2003-June 2004) is investigated from the perspective of four conceptual questions: (1) is pathological anxiety an animal, a human or a layered phenomenon with aspects of both? (2) Is anxiety a unitary or a nonunitary phenomenon? (3) What is the relationship between different aspects, or 'components', of anxiety? (4) What is the relationship between scientific and clinical concepts of anxiety? Recent findings: These questions are investigated in research papers in the areas of fear conditioning, delineation of neural pathways underlying aspects of anxiety (and anxiety disorder), and developmental plasticity. Most authors are inclined to a view in which both animal and human aspects are recognized and combined in some way (ad 1). Investigators are predominantly inclined to a nonunitary view, against the background model of multiple overlapping brain circuits (ad 2). The language of causal interaction between reified subsystems is avoided, leaving undiscussed the issue of the unity of brain functioning and the relationship of neural function and subjective experience (ad 3). The dominant framework seems to be noneliminative physicalist. There is a widely acknowledged conceptual gap between clinical and scientific understanding; however, newer methodologies enable a broader understanding, by taking into account that environmental factors play an important role in brain development and that study of regional circuitry is needed above study of neural loci (ad 4). Summary: There is a paucity of papers on purely conceptual issues. The rich phenomenology of anxiety should serve as an incentive to deeper understanding. Conceptual rigor and refinement may have an important impact upon fundamental empirical research.