The Organians were first introduced in Errand of Mercy (1967), set over one hundred years after the date of this episode. The parting prediction in this episode that they would not make official first contact with Humans for 5,000 years would prove untrue.
The Cardassians are mentioned in this episode for the only time in the series. A Cardassian corpse made a brief on-screen appearance in Dead Stop (2002), but was not identified as such (as first contact with Cardassians had not yet taken place).
The title refers to the fact that the very act of observing a process, system, or living being changes its character or nature, making the observer part of the process and changing the end results of the observations.
This is one of the rare episodes of the entire Star Trek franchise which doesn't feature any credited guest stars, with the credits proceeding straight into the production staff after the opening titles.
When trying to break the lock-out code of the decon chamber, Hoshi says that math is just another language. With that, she repeats the same opinion T'Pol has once voiced in Vox Sola (2002), when Hoshi was struggling with the equations of an alien language. The fact that she succeeds in this instance shows that she has evidently mastered the "language" of math in the meantime.