Ask five studios what a brand system includes and you will get five different lists, most of them shaped by what that studio enjoys making. It is a genuinely unhelpful situation for a buyer, because the word appears in every proposal and means something different in each one.
So here is a concrete list. Not everything on it is necessary for every company, and we will say where. But if you are paying for a system and something here is missing without a stated reason, it is fair to ask why.
The parts that define the brand
A positioning statement
One or two sentences covering who the product is for, what it replaces, and the one thing you want remembered. This is not a tagline and it is not written for customers. It exists so that every subsequent decision has something to be judged against. Without it, design reviews become taste arguments, because there is no shared standard to appeal to.
The logo, and its full set of files
The mark, plus every lockup and format. Stacked and horizontal versions, each spaced individually rather than scaled from a single file, because optical spacing does not survive being scaled. A standalone mark for square contexts. Single-colour and reversed variants for print, embroidery and dark backgrounds. SVG for the web, PDF or EPS for print, PNG at a few sizes for people who will paste into a document, and a full favicon set including the maskable Android icon.
Clear space and minimum size rules belong here too, and they should be expressed in units of the mark itself, so they survive scaling. A rule stated in millimetres stops being meaningful the moment somebody uses the logo on a screen.
A colour palette with defined jobs
Not a row of swatches. Each colour needs a stated job: this one is the brand colour, this one is for interactive elements, this one is for destructive actions, these are the surfaces text sits on. Without jobs, you get charts where the brand colour means nothing and error states in a shade nobody chose.
The palette should also include text-safe variants. Most brand colours fail contrast requirements against light backgrounds at body text sizes, which is not a flaw in the colour, it is a fact about saturation and value. The fix is a darker variant of the same hue with the rule written down: under a certain size, use the darker value. If your palette has no such variant, either nobody checked or somebody checked and decided not to tell you.
A type scale
Families, weights, sizes, line heights and letter spacing for each level: page heading, section heading, subheading, body, small print, and whatever your product needs beyond that. Six defined steps is plenty; twelve is a scale nobody can hold in their head, which means people will approximate, which is where four nearly-identical heading sizes come from.
Include the licence details. A surprising number of handovers include fonts the client has no right to use, because the licence was bought in the studio's name. Fonts should be licensed to you, in your name, covering the number of users and the kind of use you actually have.
Layout and spacing rules
A grid, a spacing scale, and stated margins for the formats you use most. This is the least glamorous part of a system and probably the one that does the most work, because inconsistent spacing is what makes a set of otherwise correct materials feel unrelated.
The parts that make it get used
Everything above is decisions. On its own it changes nothing, because under deadline pressure people do not consult decisions, they copy the last file. So the second half of a system is the manufacturing.
Templates for the things you produce weekly
A deck template built on real master slides, with theme-level styles, so changing the theme updates every slide. Social templates at the correct sizes for the platforms you actually post to. An email template. Document and invoice templates. Whatever your company makes more than once a month should exist as a template with the correct values already in it.
This is the single highest-leverage part of the whole exercise. A template makes the correct choice the fastest choice, and that is the only mechanism that reliably survives a busy week.
Design tokens, if you build software
Colour, type, spacing, radius and motion values exported in a format your developers can import: CSS custom properties, JSON, or whatever your stack expects. Named semantically, so the token describes the job rather than the value. A token called --color-surface-raised survives a palette change; one called --color-light-grey-2 does not.
Written documentation with reasoning
Twenty to thirty pages is usually right for a company of under a hundred people. The critical feature is not length, it is that each rule sits next to the reason for it. A rule without a reason gets broken the first time it is inconvenient, because nobody can evaluate whether this is a legitimate exception. A rule with a reason attached lets a competent person make a good decision in a situation you did not anticipate, which is the entire point.
The document should also cover the failure cases: what to do when a headline will not fit, what happens when a photograph arrives at the wrong ratio, how to handle a partner logo next to yours. These are the questions people actually have, and they are almost never addressed in a manual that spends nine pages on logo clear space.
A handover that includes a human
A folder is not a handover. There should be a walkthrough session, recorded, so the person hired in eight months can watch it instead of guessing. There should be a file inventory explaining what each folder contains. And there should be a named owner on your side, because a system with no owner is a system that quietly stops being current.
What you probably do not need
Some things get sold as part of a system that rarely earn their cost for a small company. A custom typeface, unless type is central to what you sell. A photographic art direction manual, if you do not commission photography. An illustration library, which is expensive to build and then expensive to extend, and which usually ends up applied to two pages. A brand book as a printed artefact.
The test is the same for each: will this be used more than twice in the next year by somebody other than the people who made it? If the honest answer is no, spend the money on templates instead.