Fluid therapy is ubiquitous in the care of critically ill patients. Available fluids for critical care clinicians can be broadly classified as crystalloid or colloid. Crystalloids may be further differentiated as balanced or unbalanced. Preferential use of balanced crystalloids may help to prevent acute kidney injury in situations where large volumes of crystalloid are being administered. Colloids are used less frequently for volume resuscitation but may be helpful in the treatment of septic shock. Concentrated albumin solutions have more limited indications and are most often used for critically ill patients with liver failure. When administering fluid to critically ill patients for volume resuscitation, volumes are typically given in 250–1000 mL aliquots. For sepsis, international guidelines recommend that patients should receive 30 mL/kg of fluid for initial therapy. This large fluid bolus is debated in the critical care community and may not be appropriate for every patient. Clinicians should use dynamic monitoring to assess fluid responsiveness as opposed to just blood pressure monitoring alone. Fluid overload can be harmful, and studies have demonstrated that higher fluid balances are associated with mortality. It is essential that clinicians assess when fluids are no longer necessary and de-resuscitate patients that are volume overloaded.