Animal sentience (AS) has evolved from a philosophical concept to a robust scientific field grounded in neuroanatomy and physiology, with profound ethical and legal implications. The aim of this work is to update the concept of AS from a biological perspective and contrast philosophical currents and their impact on legislation. A narrative bibliographic review was conducted in databases (Medline, Scopus and Lilacs) and legal repositories, analyzing literature on the neurobiology of consciousness, bioethics, and animal law. AS is scientifically grounded in the presence of a centralized nervous system, complex behaviors, and non-reflexive physiological responses. This knowledge has driven the formal recognition of AS in various legal frameworks and the adoption of ethical principles in research. Philosophically, the debate integrates the minimization of suffering, inherent rights, and the capabilities approach. Current neurobiological evidence expands the circle of moral consideration, shifting animals from being considered mere property to individuals with their own interests, requiring a constant update of normative and ethical frameworks.

KEY WORDS: Animal ethics; Non-human animals; Animal sentience; Pain; Bioethics.