A vascular access port (1100, 1200, 1300, 1400, 1500, 1600, 1700, 2000, 2100, 2200, 2300, 2400, 2500) comprising: a base (1102, 1202, 1302, 1402, 1602, 1702, 2002, 2102, 2202, 2302, 2402, 2502) configured to be attached to a vessel, the base extending in at least a longitudinal direction and a lateral direction that are orthogonal to each other, wherein at least a portion of the base is configured to contact the vessel when the base is attached to the vessel; a body (1104, 1704, 2204, 2304, 2404, 2504) extending away from the base in at least a vertical direction that is orthogonal to each of the longitudinal and lateral directions, wherein a height of the body in the vertical direction is sufficiently small to permit the entire port to remain beneath an outer surface of skin after the port has been implanted in a patient; and a guidance passageway (1130, 2030, 2130) that is at least partially defined by the body, the guidance passageway comprising a funnel region (1132, 1232, 1432, 1532, 1632, 1732 2032, 2132, 2232); characterized in that: the port is configured to be attached to the outer surface of the vessel; the funnel region decreases in size from a proximal end of the guidance passageway to a distal end of the guidance passageway, wherein the distal end of the guidance passageway defines an opening through a bottom surface of the port through which an access device can be advanced through a sidewall of the vessel into a lumen of the vessel when the port is attached to the out surface of the vessel; and wherein a periphery of the opening comprises a forward end and a rearward end and further comprises opposing sides that provide a spacing between the forward and rearward ends and define a longitudinally elongated region, wherein the guidance passageway and the longitudinally elongated region of the opening are configured to permit insertion of an access device through the port at a variety of angles relative to the bottom surface of the base, and wherein the forward and rearward ends of the opening are configured to interact with an access device to define a minimum angle at which no binding of the access device occurs. a base (1102, 1202, 1302, 1402, 1602, 1702, 2002, 2102, 2202, 2302, 2402, 2502) configured to be attached to a vessel, the base extending in at least a longitudinal direction and a lateral direction that are orthogonal to each other, wherein at least a portion of the base is configured to contact the vessel when the base is attached to the vessel; a body (1104, 1704, 2204, 2304, 2404, 2504) extending away from the base in at least a vertical direction that is orthogonal to each of the longitudinal and lateral directions, wherein a height of the body in the vertical direction is sufficiently small to permit the entire port to remain beneath an outer surface of skin after the port has been implanted in a patient; and a guidance passageway (1130, 2030, 2130) that is at least partially defined by the body, the guidance passageway comprising a funnel region (1132, 1232, 1432, 1532, 1632, 1732 2032, 2132, 2232); characterized in that: the port is configured to be attached to the outer surface of the vessel; the funnel region decreases in size from a proximal end of the guidance passageway to a distal end of the guidance passageway, wherein the distal end of the guidance passageway defines an opening through a bottom surface of the port through which an access device can be advanced through a sidewall of the vessel into a lumen of the vessel when the port is attached to the out surface of the vessel; and wherein a periphery of the opening comprises a forward end and a rearward end and further comprises opposing sides that provide a spacing between the forward and rearward ends and define a longitudinally elongated region, wherein the guidance passageway and the longitudinally elongated region of the opening are configured to permit insertion of an access device through the port at a variety of angles relative to the bottom surface of the base, and wherein the forward and rearward ends of the opening are configured to interact with an access device to define a minimum angle at which no binding of the access device occurs. the port is configured to be attached to the outer surface of the vessel; the funnel region decreases in size from a proximal end of the guidance passageway to a distal end of the guidance passageway, wherein the distal end of the guidance passageway defines an opening through a bottom surface of the port through which an access device can be advanced through a sidewall of the vessel into a lumen of the vessel when the port is attached to the out surface of the vessel; and wherein a periphery of the opening comprises a forward end and a rearward end and further comprises opposing sides that provide a spacing between the forward and rearward ends and define a longitudinally elongated region, wherein the guidance passageway and the longitudinally elongated region of the opening are configured to permit insertion of an access device through the port at a variety of angles relative to the bottom surface of the base, and wherein the forward and rearward ends of the opening are configured to interact with an access device to define a minimum angle at which no binding of the access device occurs.