This standard describes a functional specification of the Host Controller Interface (HCI) for Universal Flash Storage (UFS). The objective of UFSHCI is to provide a uniform interface method of accessing the UFS hardware capabilities so that a standard/common Driver can be provided for the Host Controller. The common Driver would work with UFS host controller from any vendor. This standard includes a description of the hardware/software interface between system software and the host controller hardware. It is intended for hardware designers, system builders and software developers. This standard is a companion document to [UFS], Universal Flash Storage (UFS). The reader is assumed to be familiar with [UFS], [MIPI-UNIPRO], and [MIPI-M-PHY]. Clause 4 provides a brief overview of the architectural overview of UFS. Clause 5 describes the register interface of UFSHCI. Clause 6 describes the data structure used by UFSHCI. Clause 7 provides a theory of operation for UFSHCI. Clause 8 describes the error recovery process for UFSHCI.