Micropiles (also called minipiles) are small-diameter (typically 0.5 to 1.5 inches), high-capacity drilled piles used in retrofit applications where space is limited or existing structures must be preserved. The piles are drilled with small-diameter equipment that can operate in confined spaces. Drilling methods include percussion, rotary, or auger drilling. The piles are grouted and cased with steel pipe. Rock sockets extending below soil into bedrock provide high load capacity in small diameter. A single micropile typically supports 5 to 100 tons depending on length and soil conditions. Micropiles are often grouped in clusters; caps connect multiple piles to distribute loads. The installation process begins with establishing access and drilling equipment. Drilling equipment is typically smaller and quieter than conventional pile driving equipment. Drilling continues until specified depth or specified soil condition is reached. Casing and grout are installed in the drilled hole, displacing soil and creating a bond with surrounding soil. Post-grouting injects additional grout under pressure, improving the bond and increasing capacity. Micropiles are ideal for underpinning existing structures where conventional pile driving would cause excessive vibration. The cost per ton of capacity is higher than conventional piles, but total project cost may be lower when considering advantages in small spaces. Micropiles have been used successfully in dense urban areas and retrofit projects.