This guide covers medical devices and diagnostics from classification through litigation. It begins with the definitional boundary that separates devices from drugs and from unregulated software, then works through the three classes, the notification pathway most devices actually use, the approval pathway a small minority take, and the risk-based route for genuinely novel products. It sets out the preemption architecture those pathways generate, the narrow parallel claim that survives it, and the drug decisions that illuminate the same asymmetry. It covers adverse event reporting and the public databases that should be searched before any complaint is drafted, the recall system and what a recall does and does not prove, the quality system requirements that supply most viable claims, and the laboratory certification regime governing diagnostics. It closes with software, promotion, evidence preservation, and working sequences for both sides.