Questions about transitioning from a monogamous to an "open" relationship

 And I apologize in advance for not knowing the correct terminology to use here (please feel free to educate me). When I say transitioning to an "open" relationship, I mean any relationship that previously involved two people as a monogamous couple, where now one or both parties is able to engage in a physically and/or emotionally intimate relationship with one or more “new” people outside of the previously established relationship. For the purposes of the questions I’m about to ask, this definition doesn’t apply to a couple which has jointly taken on a third party (or another couple) to be added to their existing relationship (but I welcome responses from people of all experiences).

So, for people who have been involved in relationships that have gone through such a transition (either as a member of the couple, or as the new party), I am curious about the following:

- Were both members of the couple allowed to pursue other individuals, or was it just one party?

- Did the decision to make the relationship open come out of a general interest in pursuing other relationships, or because one party had already found someone else of interest, and then sought permission from/agreement with the existing partner? 

- Were there difficulties with jealousies from one or both parties? Did the third person experience jealousy issues with the original relationship?

- Were there “rules” established about how the original partners could conduct their relationship? And specifically, did the rules require that the partner in the new relationship notify the other partner when such liaisons were occurring?

- If you were the other partner, would you *want* to know when such liaisons were occurring? Why or why not?
- What if the other partner didn't want to know? Would that suggest potential jealousy issues that might cause problems down the line? Or might it be normal that someone just didn't want to know anything at all about their significant other's "extracurricular" activities? 

I don’t wish to limit the discussion in this thread to just my questions, so please feel free to share whatever thoughts and experiences you find relevant.