Kidney function assessment is fundamental in a variety of clinical settings, including tropical diseases, most of which are considered as neglected diseases. This chapter discusses the main methods for assessing renal function. Glomerular Filtration Rate (GFR) is the sum of glomerular filtration of all nephrons and reflects the overall renal function. GFR is widely accepted as the best renal function measure. Serum creatinine, a product of muscle metabolism, is 85–90% filtered in the renal tubules and represents the most frequently used and most practical marker for renal function assessment. Serum creatinine is considered a late marker of kidney injury, since its elevation occurs when there is a loss of more than 50% of renal function. Currently, the Kidney Disease Improving Global Outcomes (KDIGO) guidelines recommend the use of serum creatinine-based CKD-EPI equation to estimate renal function in clinical practice. Tubular function comprises the reabsorption and secretion of substances, predominantly water and electrolytes, in addition to regulating the mechanisms of urinary concentration and acidification. The assessment of renal tubular function has two main indications: Investigation of primary tubular diseases, detection of early tubular alterations during the course of glomerular diseases (in this case, in the context of tropical diseases, which can often cause tubulointerstitial lesions and asymptomatic tubular disorders). Kidney function assessment is of utmost importance in tropical diseases, since renal involvement is a frequent occurrence, with both glomerular and tubulointerstitial involvement.