What it involves
Requirements management is the discipline of capturing what a system actually needs to do, writing it so it can be tested rather than argued about, and keeping it traceable — to its source, to its design, and to the evidence that proves it's been met. We baseline requirements formally, manage change through a controlled process rather than informal edits, and keep the whole set current as the design inevitably moves.
Why it matters
Most programme failures trace back to a requirement — one that was ambiguous, one that drifted from its original intent across design iterations, or one that nobody could confidently say was still current. Untraceable requirements mean every stakeholder is quietly building a slightly different system, and the mismatch only surfaces at integration or acceptance, when it's expensive to fix. Good requirements management is unglamorous, and it's also the single highest-leverage thing a programme can get right early.
What you get
A structured, traceable requirements set from concept through acceptance, a defined baseline and change control process, requirements written to be verifiable rather than aspirational, and a traceability matrix linking every requirement to its source and its verification evidence.