This chapter covers ripple effects. Ripple effects occur when there are positive spillover effects beyond the beneficiary, intervention, area, or thematic focus. They can be considered unintended if the donor or implementing agency did not consider that these spillovers could happen in its formal evaluation parameters. This chapter covers three kinds of ripple effects: thematically synergetic effects, catalytic effects, and human interaction effects. Thematically synergetic effects occur when a positive effect of an external intervention in one thematic area crosses over to another thematic area. Catalytic effects occur when the external intervention directly or indirectly contributes to additional development impacts in the same thematic area. Human interaction effects occur when, because of the external intervention, new social ties are created between people.