Abstract: The present invention discloses devices and methods, for non-invasive ultrasound-guided body contouring, including: a variable-frequency treatment applicator having at least one variable-frequency ultrasound emitter; and a control unit for adjusting an output frequency of at least one ultrasound emitter. Devices and methods including: a variable-frequency treatment applicator having at least one variable-frequency ultrasound emitter; a resonance sensor for determining a resonant frequency of a treatment area; and a control unit for adjusting an output frequency, of at least one ultrasound emitter, to the resonant frequency based on a signal from the resonance sensor. Devices and methods including: a variable-frequency treatment applicator having at least one variable-frequency ultrasound emitter; a cooling mechanism located in the treatment applicator; and a control unit for applying an output frequency to at least one ultrasound emitter.