Electrolyte, acid-base, and mineral metabolism disorders are among the most common and clinically significant problems experienced in internal medicine patients. Their development reflects disturbances in regulated homeostatic mechanisms involving the kidneys, bones, endocrine systems, and cellular ion transport. Disorders such as hyponatremia, hypernatremia, hypokalemia, hyperkalemia, metabolic acidosis, metabolic alkalosis, and abnormalities of calcium and phosphorus metabolism are associated with substantial morbidity and mortality when not promptly recognized and appropriately treated. Accurate diagnosis requires a deep understanding of the underlying pathophysiology, assessment of volume status, interpretation of laboratory findings, and identification of contributing kidney, endocrine, medications, and systemic factors. This review describes the physiological mechanisms governing electrolyte and acid-base homeostasis and discusses the clinical presentation, diagnostic evaluation, and evidence-based management of common electrolyte disorders encountered by Internists. We place emphasis on distinguishing etiologies and applying practical diagnostic algorithms to guide treatment decisions. In addition, the review highlights the interconnected regulation of calcium and phosphorus by parathyroid hormone, vitamin D, and fibroblast growth factor 23 and its relevance in kidney disease and other disorders. By integrating foundational physiology with current clinical practice guidelines, this review provides internists with a practical framework to solve electrolyte issues they face with confidence.