The Vortex Indicator (VI) is composed of 2 lines that show both positive (VI +) and negative (VI -) trend movement. It was inspired by certain motions found in water and was developed by Etienne Botes and Douglas Siepman. The Vortex Indicator has a relatively straight forward application: it is used by traders to identify the start of a trend. The VI + line crossing the VI - line (or a key level) could be seen as a bullish signal. The VI - line crossing the VI + line (or a key level) could be seen as a bearish signal. These are key trend change points. The indicator is often used in combination with other signals.