Due to their varying axial tilts, the planets of the Solar System are never completely aligned. However, they do sometimes get close enough to be called an alignment. Planetary alignments as seen from the Earth are more common.
Astronomers define an alignment as varying levels of proximity between the planets. Universe Today reports that the planets all come within 90 degrees of each other roughly once every 200 years. According to Universe Today, a relatively close alignment of Saturn, Venus, Jupiter and Mars, as seen from Earth, should occur in September 2040.