In X4, “quests” are commonly referred to somewhat interchangeably as “plots”, “story lines” or “story quests” (or some combination of those). These are multi-step scripted mission trees that both provide both entertainment (something to do) and an end result (something changing about the political/military state of the galaxy based on your decisions).
Each is independent, and all are optional, though some do require another to be completed before starting (see requirements to find/start story lines in the Summary section).
Story lines are X4’s attempt at putting some story-driven activities into the game for people who are interested, but are not a main focus of the game. They add challenge and flavor, but don’t unlock new functions or gameplay.
Completing a story line generally results in a shift in standing, organization, or status among the various factions in the game. With no diplomacy system beyond player reputation, these story lines are the only real means of effecting significant changes in faction diplomacy in X4. [That said, the effects are limited; it’s not a diplomacy system.]
Note that the individual steps in a story line show up in your Missions interfaces, above your other (non-story) missions. The non-story radiant mission system is described in the Missions section.
List, with requirements
Walkthroughs
NOTE: these walkthroughs try to strike a balance between discovery and giving you tips on how to be prepared for what’s coming (e.g. when you’re about to need a scout ship vs a combat ship). The focus is on helping you avoid problems, rather than explaining every single detail of every step.
If you’re looking for the specific detail of how to get Steam achievements, etc, you’ll need to look elsewhere.
If you’re looking for “help me figure this out, and warn me about frustrating pitfalls” then this will be what you’re looking for.
Note: See the summary page for a full listing of all story lines. Write ups of the others are in progress, will be posted shortly.