Early in my career, I thought a project lifecycle was one-size-fits-all. But it wasn't until I worked on a critical railway upgrade that I discovered something deeper: you can adapt best practices from both waterfall and agile, and be creative in how you deliver. How you deliver matters just as much as what you deliver.

This project involved upgrading a unique train which was responsible for inspecting the safety of London Underground tracks. The problem? We couldn't take it out of service for an extended period, as it had a special schedule to inspect the condition of the tracks. The safety of the railway depended on it.

We were working in a tight, waterfall environment. Standard practice said: plan everything upfront, execute in sequence, deliver at the end. But that wouldn't work here.

So we adapted. We borrowed from agile thinking, created a backlog of upgrades, and planned "pit stops" between inspection runs. These were short bursts of focused work where we tackled what we could based on priority. What didn't get done rolled into the next window.

It wasn't textbook anything. But it worked. We kept the train running, delivered the upgrades, and kept everyone safe. That experience taught me that project lifecycles aren't just academic concepts. As a PM, you can be creative and borrow the best from different approaches to keep things moving with purpose.

What Is a Project Lifecycle?

The Association for Project Management (APM) defines a project lifecycle as: “A framework comprising a set of distinct high-level stages required to transform an idea or concept into reality in an orderly and efficient manner."

Let me translate that: a project lifecycle is the series of stages your project goes through from the initial idea to final closure. Every project, regardless of size or type, follows some kind of journey, typically moving through initiation (getting started), planning (working out how), execution (doing the work), and closure (wrapping up). These stages give your project its shape and rhythm. The specific stages and how you move through them, whether that's in a straight line, in repeated cycles, or as a hybrid approach, that's what we call your lifecycle model. It's the framework that helps teams navigate from concept to completion without losing their way.

Making Lifecycles Real: The Family Holiday

Linear is also known as waterfall. It's called waterfall because work flows in one direction, like water flowing down steps. You complete one stage fully before moving to the next, and you don't go backwards. It's a straightforward, step-by-step approach.

Let's see this with building an office block:

Initiation: Developer identifies need, secures funding, gets initial planning permission. The project is approved to proceed.

Planning: Architects design the building, structural engineers calculate loads, planners create schedules, contractors price the work. Everything is mapped out before construction begins.

Execution & Monitoring: Ground breaks, foundations go in, structure rises floor by floor, systems get installed. Progress is tracked against the plan, but the sequence is fixed. You can't fit windows before the walls exist.

Closure: Final fit-out completed, building tested and certified, snagging issues resolved, handover to client. Accounts settled, lessons documented, maintenance contracts begin.

Each stage has clear outputs before the next can begin. You can't pour concrete before designs are approved. The lifecycle keeps everything sequenced and accountable.

Best for: Fixed requirements, physical builds, regulated environments where change is expensive or dangerous.

Why Lifecycles Matter

More than just a step-by-step guide, a lifecycle gives you:

Structure: Everyone knows which stage you're in and what comes next. This shared understanding prevents confusion and missed handoffs.
Visibility: You can anticipate typical risks and decisions for each stage. No nasty surprises.
Control: Natural checkpoints let you assess progress and adjust course before small issues become big problems.
Reflection: Stage transitions create moments to capture what worked and what didn't. This is how teams improve.

Here's what I learned on that railway project: when pressure hits, a clear lifecycle stops you drowning in complexity. You focus on what the current stage needs rather than juggling everything at once.

The Three Core Lifecycle Models

Linear (Waterfall)

Structured, step-by-step, and sequenced. You finish one stage before starting the next.

Let's see this with building an office block:

Initiation: Developer identifies need, secures funding, gets initial planning permission. The project is approved to proceed.

Planning: Architects design the building, structural engineers calculate loads, planners create schedules, contractors price the work. Everything is mapped out before construction begins.

Execution & Monitoring: Ground breaks, foundations go in, structure rises floor by floor, systems get installed. Progress is tracked against the plan, but the sequence is fixed. You can't fit windows before the walls exist.

Closure: Final fit-out completed, building tested and certified, snagging issues resolved, handover to client. Accounts settled, lessons documented, maintenance contracts begin.

Each stage has clear outputs before the next can begin. You can't pour concrete before designs are approved. The lifecycle keeps everything sequenced and accountable.

Best for: Fixed requirements, physical builds, regulated environments where change is expensive or dangerous.

Iterative (Agile)

Iterative approaches, commonly called agile, break work into small, repeatable cycles called sprints. Instead of planning everything upfront, you deliver working pieces quickly, get feedback, and adjust as you go.

Take developing a new banking app:

Initiation: Business case approved, initial user research completed, development team assembled. High-level vision defined.

Planning: Create a product backlog of features, prioritise what matters most to users, plan the first sprint. Unlike waterfall, you only plan in detail for the immediate future.

Execution & Monitoring (via Sprints):

Sprint 1: Basic login and account view. Release to test users.
Sprint 2: Add balance checking based on feedback. Release again.
Sprint 3: Include payment functionality. Test and refine.
Sprint 4: Add budgeting features users requested.
Continue: Each two-week sprint adds value, responds to feedback.

Closure: When the product meets its goals or the budget runs out. Final handover to support teams, documentation completed, team retrospective held.

There's no "big bang" release. Each cycle delivers something usable, learns from real users, and adapts the plan based on what you discover. The magic happens in the execution phase through these repeated sprints.

Best for: Fast-moving environments, digital products, evolving requirements where user feedback shapes the direction.

Hybrid

The hybrid lifecycle recognises that some projects need different approaches for different parts. It combines the predictability of waterfall where you need it with the flexibility of agile where that works better.

Consider implementing a new hospital system:

Initiation: Hospital board approves digital transformation, budget secured, regulatory requirements identified. Clear boundaries set for what must be fixed versus what can flex.

Planning: Two-track approach designed. Critical infrastructure and compliance elements follow strict waterfall planning. User-facing elements planned for iterative development. Both tracks coordinated through integrated schedule.

Execution & Monitoring:

Waterfall element: Infrastructure setup, security compliance, data migration follow strict sequential phases. Can't compromise on patient safety or data protection.
Agile element: User interface developed in sprints with feedback from doctors, nurses, admin staff, and technicians. Training materials evolve based on each department's needs. Quick adjustments based on real use.

Closure: System goes live in phases. Infrastructure signed off through formal testing. User elements refined until adoption targets met. Full handover includes both technical documentation and evolved training materials.

The backbone follows waterfall for safety and compliance. The user-facing elements iterate based on real-world use. Different speeds for different needs, all coordinated through careful integration management.

Best for: Complex projects with both rigid and flexible components, especially where regulations meet user experience.

The Reality for Project Managers

Here's what the textbooks don't always tell you:

You might not get to choose. In most organisations, the delivery model is set at strategic level. As a PM, you inherit it. Your job is to make it work.

You'll need to translate constantly. Not everyone speaks "lifecycle language." You need to make theory practical and relatable for your team.

Stages aren't always sequential. In a linear lifecycle, theory says you plan, then build, then test in clear sequence. In practice, you might discover critical requirements during build where testing reveals gaps requiring design updates. You don't restart the whole lifecycle, you handle what's needed while keeping the project moving forward.

Multiple lifecycles coexist. In cross-functional work, one team might use agile methods while another follows waterfall. Managing that mix requires deliberate coordination, not just hope.

That railway project taught me this: you can be adaptive and creative within your constraints. Real delivery is about making the lifecycle work for you, not against you.

Mixing and Matching Without Chaos

Even in structured environments, you can bring in tools from other lifecycles:

Daily stand-ups: Surface blockers early, even in waterfall. Five minutes can save five days.

Retrospectives: Not just for agile. Pause at milestones to ask "what did we learn?"

Backlogs: When scope inevitably expands, keep a visible, prioritised list.

Stage gates: Checkpoint reviews keep fast-moving work aligned with strategy.

Kanban boards: Visualise progress and bottlenecks in any lifecycle.

User story mapping: Helps teams understand the "why" behind features.

Timeboxing: Prevents analysis paralysis and forces decisions.

The trick isn't to follow fashion. It's to pick tools that create clarity, maintain momentum, and deliver outcomes. I've seen teams fail because they adopted practices that looked good but didn't fit their reality.

Key Takeaways

Project lifecycles provide the structure that underpins successful delivery
There's no one-size-fits-all. The best PMs adapt what works for their context
Linear gives rigid structure, iterative gives flexible structure, hybrid attempts balance
You won't always choose the project lifecycle, but you can influence how it's applied
Borrow tools that enhance visibility and control within your structure
Real delivery often blurs the textbook boundaries, and that's okay
Your reflection: What lifecycle are you working in? More importantly, is the structure helping or hindering your delivery?

Project delivery isn't about perfect process. It's about finding the structure that supports your reality.

When things go wrong (and they will), your lifecycle can either provide a framework to help you recover or become another constraint. The real skill is knowing how to work within your structure while staying focused on what needs to be delivered.

References

Association for Project Management - What is a life cycle?

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Project Lifecycles: The Structure Behind Successful Delivery