This article examines key parameters that contribute to amplifier noise. It explains how amplifier design, specifically the choice of bipolar, JFET-input, or CMOS-input design, affects noise. The note also explains how to select a low-noise amplifier for low-frequency analog applications such as buffering data converters, amplifying strain-gauge signals, and preamplifying microphone outputs. The CMOS-input based amplifier, MAX4475, illustrates the benefits of using this newer amplifier design for many lower frequency analog applications.