This chapter is devoted to propulsion ideas that are considered for future interplanetary mission applications. Starting with a discussion of the limitations of chemical rockets, a review of other energy sources provides a perspective for future propulsion, and description of nuclear rockets, including formulas and performance parameters to assess their potential for interplanetary applications, focusing on near-term nuclear thermal propulsion. To present a perspective on other ideas, the last sections are devoted to futuristic propulsion concepts that require other energy sources and for which we lack today crucial technologies. Since I cannot predict the future for astronautics, I wrote a Postscript to expand on technology challenges to advance propulsion capable of fast interplanetary voyages. I am certain that future generations of engineers and scientists will develop and build the as-yet imagined spaceships that will take us to the stars.