Disclosed herein are various deflectable catheter systems that utilize materials having negative coefficients of thermal expansion to cause the catheter to deflect. A representative embodiment of the present invention includes a catheter having a heat-sensitive control member located outside the distal end of the catheter, but which is in mechanical communication with the distal end of the catheter such that heat may be applied to the control member to cause the distal portion to deflect. The applied heat, however, does not introduce any significant heat into the distal end of the catheter. The system may also include a processor to estimate an amount by which the catheter has been deflected based in part on temperature information of the control member, or even resistance measurements for the control member. The system may also include calibration systems and methods. Also disclosed herein are methods of use and methods of manufacturing system that utilize materials having negative coefficients of thermal expansion as control members.