A high-density mapping catheter comprising the following: a catheter shaft comprising a proximal end and a distal end, the catheter shaft defining a catheter shaft longitudinal axis extending between the proximal end and the distal end; a flexible tip portion located adjacent to the distal end of the catheter shaft, the flexible tip portion comprising a flexible framework comprising nonconductive material; and a plurality of microelectrodes mounted on the flexible framework and forming a flexible array of microelectrodes adapted to conform to tissue, wherein the microelectrodes are ring electrodes; wherein the flexible framework is configured to facilitate relative movement among at least some of the microelectrodes relative to other of the microelectrodes; and wherein the nonconductive material insulates each microelectrode from other microelectrodes; wherein the plurality of microelectrodes are mounted on the flexible framework and arranged in a plurality of groups; wherein each group of the plurality of groups of microelectrodes comprises a row of longitudinally-aligned microelectrodes aligned parallel to the catheter shaft longitudinal axis; wherein the flexible array of microelectrodes comprises a two-sided planar array of microelectrodes, wherein the microelectrodes are configured for contacting tissue on a front side and back side of the planar array; wherein the flexible framework comprises a plurality of longitudinally-extending and laterally separated arms (190, 192, 194, 188) extending parallel to the catheter shaft longitudinal axis, and lying in a plane; wherein each longitudinally-extending arm (190, 192, 194, 188) has a group of the plurality of groups of microelectrodes distributed and located thereon; wherein a proximal bushing is mounted on the distal end of the catheter shaft; wherein each longitudinally-extending arm exits from a distal end of the proximal bushing; and wherein the plurality of longitudinally-extending arms (190, 192, 194, 188) are configured to maintain the plurality of microelectrodes in the plurality of rows in a spaced relationship such that each of the plurality of microelectrodes can capture separate data about the electrical activity of cardiac tissue adjacent to the plurality of microelectrodes. a catheter shaft comprising a proximal end and a distal end, the catheter shaft defining a catheter shaft longitudinal axis extending between the proximal end and the distal end; a flexible tip portion located adjacent to the distal end of the catheter shaft, the flexible tip portion comprising a flexible framework comprising nonconductive material; and a plurality of microelectrodes mounted on the flexible framework and forming a flexible array of microelectrodes adapted to conform to tissue, wherein the microelectrodes are ring electrodes; wherein the flexible framework is configured to facilitate relative movement among at least some of the microelectrodes relative to other of the microelectrodes; and wherein the nonconductive material insulates each microelectrode from other microelectrodes; wherein the plurality of microelectrodes are mounted on the flexible framework and arranged in a plurality of groups; wherein each group of the plurality of groups of microelectrodes comprises a row of longitudinally-aligned microelectrodes aligned parallel to the catheter shaft longitudinal axis; wherein the flexible array of microelectrodes comprises a two-sided planar array of microelectrodes, wherein the microelectrodes are configured for contacting tissue on a front side and back side of the planar array; wherein the flexible framework comprises a plurality of longitudinally-extending and laterally separated arms (190, 192, 194, 188) extending parallel to the catheter shaft longitudinal axis, and lying in a plane; wherein each longitudinally-extending arm (190, 192, 194, 188) has a group of the plurality of groups of microelectrodes distributed and located thereon; wherein a proximal bushing is mounted on the distal end of the catheter shaft; wherein each longitudinally-extending arm exits from a distal end of the proximal bushing; and wherein the plurality of longitudinally-extending arms (190, 192, 194, 188) are configured to maintain the plurality of microelectrodes in the plurality of rows in a spaced relationship such that each of the plurality of microelectrodes can capture separate data about the electrical activity of cardiac tissue adjacent to the plurality of microelectrodes.