This work describes the design, fabrication, and application of an ultrastable scanning probe microscope for nanoscale studies at the solid-liquid interface, specifically in electrolyte environments. Quantification of system noise limits in the tunneling mode, mechanical drift rates, and lowest mechanical resonance provided values of < or = 10 pA/Hz(1/2), 2 nm/min (XY) and 0.15 nm/min (Z), and 7.9 kHz, respectively. Measurement of the closed-loop transfer function in the tunneling condition demonstrated linear feedback responses up to 4.2 and 2.5 kHz in ambient and electrochemical conditions. Atomic and molecular resolution imagings have been achieved in ambient, in situ, and electrochemical imaging environments at scan rates up to 80 lines/s. A modular design approach has produced a highly flexible microscope capable of imaging and spectroscopy in tunneling, tapping force [amplitude modulation atomic force microscopy (AFM)], and noncontact force (frequency modulation-AFM) modes.