The project environment consists of all those organisational elements that are necessary to define and deliver a change using project management disciplines. This definition does not seem really evident or useful to most people, because the project environment is something that they are largely unaware of. Yet, it clearly exists: if an organisation has project managers as a separate career path, they will be part of the project environment and easily identified. The same goes for the various PMOs of different sizes that may exist in the organisation. In addition, IT usually has a sizeable projects organisation. Perhaps Management Accounts in Finance will also deploy Finance Business Partners that deal solely with project work.
My argument is that the project environment is made up of all those organisational elements that contribute to the planning and execution of projects - not just those mentioned above. In some organisations, usually smaller ones, the obvious (visible) portion of the project environment could be a group of part-time project managers and nothing else. So why is the rest of the project environment invisible?
As an illustration, let's imagine an organisation that doesn't normally use projects. Imagine perhaps a Charity, that through a surprisingly generous endowment is now able to grow and extend the reach of its work. Up to now, all the work that involved changes or adding new capabilities was carried out as part of the normal operational work. People liaised with each other to coordinate whatever needed to be done jointly on an ad hoc basis.
Things are different now: growth brings complexity, a need for transparency, and the need to quantify progress. As the central team divides, new people are brought in, hierarchies are introduced and the next major project will be running in a classic matrix environment, not a purely operational environment. However, because approaching the management of change with project management disciplines is new here, it could well be that in this growing Charity the only people who talk about PM disciplines are the newly imported project managers. Everyone else just cooperates when asked. The visible project environment will be the PMs in this case, while the invisible project environment will consist of all the rest, blended and blurred into jobs that are still evolving in the new organisation. The point is that that invoices will still be processed and paid, but not by the PMs. Suppliers will develop and install new systems, not the PMs. Resources will be allocated and moved around, not by the PMs. And the SMEs in various teams will devote part of their time to project deliverables, albeit (in their own minds) as part of their day to day work. This happens because the project environment always exists, whether it is visible and obvious to everyone or not, otherwise the PMs would not be able to deliver anything.
As this Charity (or any organisation) grows, it will become self-evident to the senior managers that projects would be more certain of delivering benefits if certain aspects of the work performed in some key teams were explicitly dedicated to projects. The PMs would then spend less time negotiating every activity. It will also be evident that once you have more than a few projects running concurrently there is a need to balance priorities and juggle funds at the level of the whole organisation. That requires some dedicated focus on PM matters in central areas. This is how further sections of the project environment come into the light, little by little.
Because this "coming into the light" process is so organic in a way, so dependent on the specific history and circumstances of every organisation, the result doesn't follow any template. In fact there are grey areas: whereas PMs and PMO are definitely visible most of the time, and in contrast some areas remain quite invisible, there will be other "grey area" teams that are focused on PM matters but report to different management hierarchies.
I mentioned in passing above that most organisations will have more than one PMO, and many of those will have PMO teams at many different organisational levels, and with different remits in larger organisations. The fact is that most organisations that use PMO at all will typically have more than one. There may be PMOs within specialist areas that look after many projects in that area. Other PMOs may be embedded within large projects, some will be operating at the Programme level. Finally, more and more organisations are now formalising the management of their portfolios of change, so there will be Portfolio level PMOs. They go by quite a varied range of names. It doesn't matter. All of them, taken together, form the most visible and explicit part of the project environment of a given organisation. Their mission may revolve around being an information hub, or providing financial control, or being the home for the PM workforce, or many combinations of the above that have grown organically and politically. What they all have in common is that they bring a measure of control to the project environment - even to the invisible parts by specifying interfaces with them. And a controlled project environment leads to a better return on project investment.