A blade outer air seal assembly for a gas turbine engine comprising: a main body portion that extends generally axially, with respect to a central axis; of the gas turbine engine, from a leading edge portion of the main body portion to a trailing edge portion of the main body portion, wherein the leading edge portion includes a leading edge wall having an undercut profile, along at least a portion of the leading edge wall; at least one attachment portion (60a, 60b) coupled to the main body portion, the at least one attachment portion (60a, 60b) configured for attachment to a receiving portion, the at least one attachment portion (60a, 60b) comprising at least one leading attachment portion proximate the leading edge portion; and cooling passages defined within the main body portion, comprising a leading edge cooling passage adjacent to the leading edge wall, and a plurality of aft cooling passage axially aligned aft of the leading edge cooling passage wherein: the leading edge cooling passage has a leading edge periphery on a side of the leading edge cooling passage adjacent to the leading edge wall wherein the leading edge periphery runs substantially parallel to the undercut profile of the leading edge wall; the plurality of axially aligned aft cooling passages comprise top linear edges and bottom linear edges; the top linear edges define a ceiling line of the plurality of aft cooling passages, and the bottom linear edges define a floor line of the plurality of aft cooling passages; the leading edge cooling passage has at least a bottom edge which deviates from the floor line of the plurality of aft cooling passages; and characterised in that the leading edge periphery is configured to substantially maintain a constant distance between the leading edge cooling passage and the leading edge wall including the undercut profile; and in that the leading edge cooling passage comprises at least one of a tilted, undercut, or bent configuration with respect to the aft cooling passages such that the leading edge cooling passage projects above the ceiling line. a main body portion that extends generally axially, with respect to a central axis; of the gas turbine engine, from a leading edge portion of the main body portion to a trailing edge portion of the main body portion, wherein the leading edge portion includes a leading edge wall having an undercut profile, along at least a portion of the leading edge wall; at least one attachment portion (60a, 60b) coupled to the main body portion, the at least one attachment portion (60a, 60b) configured for attachment to a receiving portion, the at least one attachment portion (60a, 60b) comprising at least one leading attachment portion proximate the leading edge portion; and cooling passages defined within the main body portion, comprising a leading edge cooling passage adjacent to the leading edge wall, and a plurality of aft cooling passage axially aligned aft of the leading edge cooling passage wherein: the leading edge cooling passage has a leading edge periphery on a side of the leading edge cooling passage adjacent to the leading edge wall wherein the leading edge periphery runs substantially parallel to the undercut profile of the leading edge wall; the plurality of axially aligned aft cooling passages comprise top linear edges and bottom linear edges; the top linear edges define a ceiling line of the plurality of aft cooling passages, and the bottom linear edges define a floor line of the plurality of aft cooling passages; the leading edge cooling passage has at least a bottom edge which deviates from the floor line of the plurality of aft cooling passages; and characterised in that the leading edge periphery is configured to substantially maintain a constant distance between the leading edge cooling passage and the leading edge wall including the undercut profile; and in that the leading edge cooling passage comprises at least one of a tilted, undercut, or bent configuration with respect to the aft cooling passages such that the leading edge cooling passage projects above the ceiling line. the leading edge cooling passage has a leading edge periphery on a side of the leading edge cooling passage adjacent to the leading edge wall wherein the leading edge periphery runs substantially parallel to the undercut profile of the leading edge wall; the plurality of axially aligned aft cooling passages comprise top linear edges and bottom linear edges; the top linear edges define a ceiling line of the plurality of aft cooling passages, and the bottom linear edges define a floor line of the plurality of aft cooling passages; the leading edge cooling passage has at least a bottom edge which deviates from the floor line of the plurality of aft cooling passages; and characterised in that the leading edge periphery is configured to substantially maintain a constant distance between the leading edge cooling passage and the leading edge wall including the undercut profile; and in that the leading edge cooling passage comprises at least one of a tilted, undercut, or bent configuration with respect to the aft cooling passages such that the leading edge cooling passage projects above the ceiling line.