IAB Content Taxonomy Reference
Every domain in the URL Categorization Database is classified using both IAB Content Taxonomy v2 and v3, with about 700 categories per version organized across 4 hierarchical tiers. These taxonomies are the advertising industry's standard for content classification, enabling contextual targeting, brand safety, and audience segmentation at scale.
The IAB Content Taxonomy, also called the IAB taxonomy or simply IAB categories, is a tree of content topics in which every row has a stable ID. Ad requests, contextual targeting tools and brand safety rules use those IDs to say what a page, app or site is about.
Two lines are in use today: the 2.x versions (2.0 to 2.2) and the 3.x versions (3.0 and 3.1). Both go down to four tiers, from broad branches such as Sports to narrow topics such as Skiing.
What is the IAB Content Taxonomy?
The IAB (Interactive Advertising Bureau) Content Taxonomy is the advertising industry's standard for content categorization. It provides a hierarchical classification system used by advertisers, publishers, and ad tech platforms to categorize digital content for contextual targeting, brand safety, and audience segmentation.
Both IAB v2 and v3 are included in every database tier at no additional cost.
Any content taxonomy
A content taxonomy is a controlled list of topics, arranged as a tree, used to tag articles, videos, products or websites the same way every time. Publishers often keep their own for navigation and search.
The IAB Content Taxonomy
The IAB version is a shared, public tree built for advertising. Its value is that a buyer, a seller and a verification tool all read the same ID the same way.
Where it is used
Contextual targeting, brand safety and suitability, inventory reporting and supply decisions. In bid requests the categories travel as codes, together with a field that names the taxonomy version.
IAB Content Taxonomy versions compared
Six versions have been published, from the original 1.0 list to 3.1. The row counts below come from the published taxonomy files, so you can check them against your own copy.
| Version | Released | Category rows | Top-level rows | Deepest tier | What changed |
|---|---|---|---|---|---|
| 1.0 Deprecated | Original list | 392 | 26 (IAB1 to IAB26) | Tier 2 | Two-level list with codes such as IAB1-1. Deprecated since 2020, but the codes can still appear in older integrations. |
| 2.0 2.x line | November 2017 | 698 topic rows | 29 | Tier 4 | Rebuilt with numeric IDs and four tiers. The same file holds 481 extra rows for content type, format, channel, language and source. |
| 2.1 2.x line | October 2020 | 698 topic rows | 29 | Tier 4 | Same rows, with 64 flagged as sensitive category data (SCD) for privacy safeguards. |
| 2.2 2.x line | December 2020 | 715 topic rows | 31 | Tier 4 | Adds a Sensitive Topics branch with 11 rows and a Brand Suitability and Risk branch with four risk levels. |
| 3.0 3.x line | June 2022 | 703 | 36 | Tier 4 | Restructured tree for news, video and CTV, podcasts, radio, games and app stores. Descriptive rows moved to a separate Descriptive Vectors file; not compatible with 2.x lists. |
| 3.1 Current | December 2024 | 704 | 37 | Tier 4 | Adds the Thriller genre (ID 700) and tidies a few names and parents. 3.0 IDs are kept, so 3.0 lists stay valid. |
In 3.1 the Communication row (ID 80DV8O) is listed without a parent, which is why the top level counts 37 rows instead of 36. Our IAB Content Taxonomy 3.0 vs 3.1 page lists every row that moved.
Major and minor numbers
A new major number, such as 2 to 3, signals breaking changes. A minor number, such as 3.0 to 3.1, adds rows without changing the structure.
Do not mix the lines
IAB Tech Lab states that 3.0 may not be used alongside versions 1.0 to 2.2. Keep one line per list and convert at the edges of your system.
Declare the version
In OpenRTB and AdCOM the cattax field names the taxonomy behind category codes, for example 7 for Content Taxonomy 3.0 and 9 for 3.1. Check the current AdCOM list before you hard-code a value.
Respect SCD flags
From 2.1 on, rows that touch sensitive category data carry an SCD flag, 63 of them in 3.1. Treat them with care when you build audiences.
Tier Structure
The IAB taxonomy uses a 4-tier hierarchy, moving from broad categories to highly specific classifications. Each tier provides an additional level of granularity.
Not all domains have values at every tier level. Tier 1 is always present. Lower tiers are populated only when a more specific classification is available.
What each tier holds in 3.1, and how deep our labels go. The last two columns show the share of domains in our file that carry a label at that tier.
| Tier | Rows in 3.1 | Example path from the 3.1 file | Our domains, v3 | Our domains, v2 |
|---|---|---|---|---|
| Tier 1 | 37 | Sports | Every domain | Over 99.9% |
| Tier 2 | 323 | Sports > Skiing | 95.6% | 90.0% |
| Tier 3 | 275 | Travel > Travel Type > Hotels and Motels | 50.4% | 51.2% |
| Tier 4 | 69 | Business and Finance > Business > Business Banking & Finance > Private Equity | 13.6% | 13.6% |
Why most sites stop at tier 2 or 3
A label describes the whole site, not one page. A hotel booking site fits Travel > Travel Type > Hotels and Motels, while a broad portal stays at a higher tier because no narrow topic covers it.
Roll up with tier 1
Reports and dashboards usually group by tier 1, because every domain has one. Use the deeper tiers for targeting and exclusions.
Not every branch reaches tier 4
Only 69 rows in 3.1 sit at tier 4, most of them under Technology & Computing, Style & Fashion, Business and Finance and Medical Health. An empty tier 4 is normal, not missing data.
IAB Content Taxonomy v2
The 2.x line (2.0 from November 2017, 2.1 and 2.2 from late 2020) is still common in ad tech and remains the base of many programmatic integrations. It holds 698 topic categories across 4 tiers in 2.0 and 2.1, and 715 in 2.2 with the Sensitive Topics and brand suitability rows.
IAB Content Taxonomy v3
Version 3.0 (June 2022) restructured the tree to better support news, video and CTV, podcasts, radio, games and app stores, and 3.1 (December 2024) added a Thriller genre. The 3.x line is the current standard for new work.
Key differences from v2:
- Updated category names and structure
- Better coverage of modern content types (video and CTV, podcasts, radio, games)
- Improved granularity in technology and digital media categories
- Format, channel and source rows moved out of the topic tree into a separate Descriptive Vectors file
What moved between IAB v2 and v3
Most migration work sits between 2.x and 3.x, not between 3.0 and 3.1. Comparing the 2.2 and 3.0 files, six top-level branches disappeared and eleven new ones appeared.
News and Politics split up
The 2.x branch News and Politics is gone. Politics, Crime, Law and Disasters are their own top-level branches in 3.x, and War and Conflicts is new.
Entertainment gathers media
Movies, Television and Music and Audio were separate branches in 2.x. In 3.x they sit under Entertainment, so imdb.com moves from Movies in our v2 column to Entertainment > Movies in v3.
Events and Attractions split
3.x separates Attractions, such as parks, museums and casinos, from Events. Holidays and Personal Celebrations & Life Events became top-level branches.
Genres is a new branch
Style descriptors such as Comedy, Documentary or Thriller live in Genres. A 2.x row that mixed topic and style becomes a topic plus a genre in 3.x.
Planning a migration? Our IAB taxonomy mapping guide covers mapping by meaning, and the IAB Content Taxonomy 3.1 category list shows the full 3.1 tree.
v2 vs v3: Which Should I Use?
Both taxonomies are included in every database, so you do not have to choose one exclusively. Here is guidance on when each version is most appropriate.
Use v2 if:
- Your ad tech stack is built on IAB v2
- You need backward compatibility with existing systems
- Your DSP/SSP partners use v2 category IDs
Use v3 if:
- You are building a new system
- You need better coverage of modern content types
- You want the most up-to-date categorization standard
Use both if:
- You serve multiple downstream partners with different requirements
- You want maximum flexibility for category mapping
Both taxonomies are included in every database. You can use v2, v3, or both simultaneously. There is no additional cost for either.
How our data maps each domain to IAB categories
Each record holds the domain, four IAB v2 tier columns, four IAB v3 tier columns and the web filtering categories, plus personas, country and popularity fields. Values are category names, listed in the data dictionary.
- Domain
- booking.com
- IAB v2 tiers 1 to 4
- Travel > Travel Type > Hotels and Motels
- IAB v3 tiers 1 to 4
- Travel > Travel Type > Hotels and Motels
- Web Filtering Category
- Travel
- Personas (first three)
- Seasonal Wanderer; Frequent Flyer; Travel Blogger
- Global Popularity Rank Group
- 1-1000
Most common IAB v3 tier 1 categories across our file. Business and Finance and Technology & Computing together cover 42.4% of all domains, and the other branches share the rest.
Using the IAB columns in practice
- Pick the version column. Read v3 for new work and v2 for partners whose stack still expects 2.x.
- Read the deepest filled tier. It is the most specific label for the site; tier 1 is the roll-up for reports.
- Join names to official IDs if you need codes. Match each path to the published taxonomy file and record the version you used.
- Add the web filtering categories for safety rules. Exclude sensitive groups such as Adult or Gambling on the same row, as our brand safety categories guide shows.
- Spot-check before loading a full list. Run a few of your own domains through the domain categorization check to see the labels you will receive.
Using IAB Categories for Custom Web Filtering
The 58 web filtering categories included in the database provide broad content classification suitable for most filtering use cases. However, the roughly 700 IAB categories can be used to extend and refine your web filtering policies with much greater granularity.
For example, if your web filtering policy uses the broad "News/Media" category but you need more specific control, you can use IAB tier 1 and tier 2 categories to tell politics, business, technology and entertainment sites apart. This allows you to build targeted filtering rules that go far beyond the standard 58 categories.
By combining the web filtering categories with IAB tier data, you can create custom category hierarchies tailored to your organization's specific content policy requirements.
IAB Content Taxonomy and related taxonomies
IAB Tech Lab publishes several taxonomies that answer different questions. Mixing them up is a common source of wrong targeting.
Content Taxonomy
Describes what the content is about: a page, app, video or website. This is the taxonomy in our IAB columns.
Ad Product Taxonomy
Describes what an ad is selling, now in version 2.0. Our content vs ad product taxonomy page compares the two.
Audience Taxonomy
Names audience segments by demographics, interests and purchase intent, currently version 1.1. It labels people segments, not content.
Web filtering categories
Our own set of 58 categories for security and access policies, delivered on the same record. See the web filtering categories reference.
IAB taxonomy terms in one place
The published files and bid request specs use a small set of terms. Knowing them makes the official files easy to read.
Unique ID
The stable code of a row, such as 627 for Search in the 3.x files. Store IDs rather than names when you exchange lists with partners.
Parent
The ID of the row one tier up. Following parents from any row leads back to its tier 1 branch.
Tier 1 to Tier 4
The four name columns of the file. Together they spell the full path of a row, such as Travel > Travel Type > Hotels and Motels.
SCD
Sensitive category data. A flag in the extension column of 2.1 and later marks rows that need extra care.
Descriptive Vectors
The 3.x companion file for content type, format, channel and source, kept apart from the topic tree.
cattax
The OpenRTB and AdCOM field that says which taxonomy a list of category codes comes from.
Common mistakes with IAB categories
These six errors are behind many broken segments and rejected category lists. Each one is easy to avoid once you know it.
IAB Content Taxonomy FAQ
What is the IAB Content Taxonomy?
It is a hierarchical list of content categories, each with a stable ID, maintained by IAB Tech Lab. IAB stands for Interactive Advertising Bureau.
Publishers, ad platforms and brand safety tools use it to describe what a page, app, video or website is about, mainly for contextual targeting and brand safety.
What is the latest version of the IAB Content Taxonomy?
Version 3.1, released in December 2024. It is a minor update to 3.0 from June 2022 that adds a Thriller genre and keeps the 3.0 IDs, so lists built on 3.0 stay valid.
What is the difference between IAB v2 and IAB v3?
Version 3.0 restructured the tree. Politics, Crime, Law and Disasters became top-level branches, Movies, Television and Music moved under Entertainment, and format rows moved to a separate Descriptive Vectors file.
IAB Tech Lab states that 3.0 may not be used alongside versions 1.0 to 2.2, so one list should use one line or the other.
How many IAB categories are there?
Version 3.1 has 704 rows: 37 at the top level, 323 at tier 2, 275 at tier 3 and 69 at tier 4. The 2.0 and 2.1 files hold 698 topic rows plus 481 descriptive rows, and the old 1.0 list has 392 rows under 26 tier 1 codes.
What are IAB tiers?
Tiers are the levels of the tree. Tier 1 is the broad branch, such as Technology & Computing, and each lower tier narrows it, down to tier 4, such as Technology & Computing > Computing > Internet > Search.
Not every branch goes down to tier 4.
Does your database use IAB v2 or IAB v3?
Both. Every domain carries one IAB v2 path and one IAB v3 path with up to four tiers, next to the 58 web filtering categories, so you can serve partners on either version from the same file.
Both IAB versions on every domain
License 120 million categorized domains with IAB v2 and v3 tiers and the 58 web filtering categories in one file, for your own systems.