Population aging challenges healthcare systems, requiring gerontological advanced practice nurses (GAPN) to address specific and complex care requirements of older adults. GAPN implement evidence-based practices directed to patients and families, focusing on health promotion and protection, disease prevention, recovery, and rehabilitation. In competence-based gerontological advanced practice, comprehensive geriatric assessment is essential for implementing the care plan. In this theoretical essay we reflect about the role of assessment in competence-based advanced nursing practice directed to the care of older adults. From our perspective, geriatric assessment for a high-quality practice must be comprehensive, multidimensional, interdisciplinary, and planned. GAPN must have solid competencies for clinical skills and caring practices; education for health literacy; collaborative care; system management for continuity of care; ethics, advocacy, and moral agency; and evidenced-based practice inquiry. Gerontological models of care and GAPN competencies serve as frameworks to guide practice while assessment is fundamental for providing age-friendly care to older adults.