diff --git a/rfcs/0000-observable-field-set.md b/rfcs/0000-observable-field-set.md
new file mode 100644
index 0000000000..ac968f45fc
--- /dev/null
+++ b/rfcs/0000-observable-field-set.md
@@ -0,0 +1,149 @@
+# 0000: Observable Field Set
+<!-- Leave this ID at 0000. The ECS team will assign a unique, contiguous RFC number upon merging the initial stage of this RFC. -->
+
+- Stage: **0 (strawperson)** <!-- Update to reflect target stage. See https://elastic.github.io/ecs/stages.html -->
+- Date: **TBD** <!-- The ECS team sets this date at merge time. This is the date of the latest stage advancement. -->
+
+<!--
+As you work on your RFC, use the "Stage N" comments to guide you in what you should focus on, for the stage you're targeting.
+Feel free to remove these comments as you go along.
+-->
+
+<!--
+Stage 0: Provide a high level summary of the premise of these changes. Briefly describe the nature, purpose, and impact of the changes. ~2-5 sentences.
+-->
+
+This RFC proposes the addition of a new field set named observable to the Elastic Common Schema (ECS). The goal of this field set is to provide a structured way to describe cyber observables that are observed in network and host events and alerts, and cyber threat intelligence. Cyber observables are raw artifacts that can be observed in network traffic, system logs, or other data sources. This field set closely aligns with the [`threat field set`](https://github.com/elastic/ecs/blob/main/rfcs/text/0008-threat-intel.md) but because not every observable is an indicator, or may be designated one
+over the course of an investigation, its main goal is to aid in tracking and investigating them. When determining what 
+fields are required, using the [STIX Cyber Observable data model](https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_mlbmudhl16lr) as guidance is recommneded as most security systems provide observables in this structure. 
+
+<!--
+Stage 1: If the changes include field additions or modifications, please create a folder titled as the RFC number under rfcs/text/. This will be where proposed schema changes as standalone YAML files or extended example mappings and larger source documents will go as the RFC is iterated upon.
+-->
+
+<!--
+Stage X: Provide a brief explanation of why the proposal is being marked as abandoned. This is useful context for anyone revisiting this proposal or considering similar changes later on.
+-->
+
+## Fields
+
+The following fields were added as a starting point and to aid in the understanding of the field set. These fields were
+closely modeled using the [STIX Cyber Observable data model](https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_mlbmudhl16lr) and the existing [`threat.indicator.*`](https://github.com/elastic/ecs/blob/main/schemas/threat.yml#L345) fields.
+
+```text
+observable.description
+observable.domain
+observable.email.address
+observable.first_seen
+observable.id
+observable.ip
+observable.last_seen
+observable.modified_at
+observable.name
+observable.port
+observable.provider
+observable.reference
+observable.spec_version
+observable.type
+```
+
+Like the threat field set, the following field sets make sense for field reuse:
+
+```
+observable.as.*
+observable.file.*
+observable.geo.*
+observable.registry.*
+observable.url.*
+observable.x509.*
+```
+
+<!--
+Stage 1: Describe at a high level how this change affects fields. Include new or updated yml field definitions for all of the essential fields in this draft. While not exhaustive, the fields documented here should be comprehensive enough to deeply evaluate the technical considerations of this change. The goal here is to validate the technical details for all essential fields and to provide a basis for adding experimental field definitions to the schema. Use GitHub code blocks with yml syntax formatting, and add them to the corresponding RFC folder.
+-->
+
+<!--
+Stage 2: Add or update all remaining field definitions. The list should now be exhaustive. The goal here is to validate the technical details of all remaining fields and to provide a basis for releasing these field definitions as beta in the schema. Use GitHub code blocks with yml syntax formatting, and add them to the corresponding RFC folder.
+-->
+
+## Usage
+
+<!--
+Stage 1: Describe at a high-level how these field changes will be used in practice. Real world examples are encouraged. The goal here is to understand how people would leverage these fields to gain insights or solve problems. ~1-3 paragraphs.
+-->
+
+## Source data
+
+<!--
+Stage 1: Provide a high-level description of example sources of data. This does not yet need to be a concrete example of a source document, but instead can simply describe a potential source (e.g. nginx access log). This will ultimately be fleshed out to include literal source examples in a future stage. The goal here is to identify practical sources for these fields in the real world. ~1-3 sentences or unordered list.
+-->
+
+<!--
+Stage 2: Included a real world example source document. Ideally this example comes from the source(s) identified in stage 1. If not, it should replace them. The goal here is to validate the utility of these field changes in the context of a real world example. Format with the source name as a ### header and the example document in a GitHub code block with json formatting, or if on the larger side, add them to the corresponding RFC folder.
+-->
+
+<!--
+Stage 3: Add more real world example source documents so we have at least 2 total, but ideally 3. Format as described in stage 2.
+-->
+
+## Scope of impact
+
+<!--
+Stage 2: Identifies scope of impact of changes. Are breaking changes required? Should deprecation strategies be adopted? Will significant refactoring be involved? Break the impact down into:
+ * Ingestion mechanisms (e.g. beats/logstash)
+ * Usage mechanisms (e.g. Kibana applications, detections)
+ * ECS project (e.g. docs, tooling)
+The goal here is to research and understand the impact of these changes on users in the community and development teams across Elastic. 2-5 sentences each.
+-->
+
+## Concerns
+
+<!--
+Stage 1: Identify potential concerns, implementation challenges, or complexity. Spend some time on this. Play devil's advocate. Try to identify the sort of non-obvious challenges that tend to surface later. The goal here is to surface risks early, allow everyone the time to work through them, and ultimately document resolution for posterity's sake.
+-->
+
+<!--
+Stage 2: Document new concerns or resolutions to previously listed concerns. It's not critical that all concerns have resolutions at this point, but it would be helpful if resolutions were taking shape for the most significant concerns.
+-->
+
+<!--
+Stage 3: Document resolutions for all existing concerns. Any new concerns should be documented along with their resolution. The goal here is to eliminate risk of churn and instability by ensuring all concerns have been addressed.
+-->
+
+## People
+
+The following are the people that consulted on the contents of this RFC.
+
+* @brett-fitz | author
+
+<!--
+Who will be or has been consulted on the contents of this RFC? Identify authorship and sponsorship, and optionally identify the nature of involvement of others. Link to GitHub aliases where possible. This list will likely change or grow stage after stage.
+
+e.g.:
+
+* @Yasmina | author
+* @Monique | sponsor
+* @EunJung | subject matter expert
+* @JaneDoe | grammar, spelling, prose
+* @Mariana
+-->
+
+## References
+
+<!-- Insert any links appropriate to this RFC in this section. -->
+
+* [RFC 0008: Cyber Threat Intelligence Fields](https://github.com/elastic/ecs/blob/main/rfcs/text/0008-threat-intel.md)
+* [OpenCTI Elastic threat intelligence integration with observable field set](https://docs.elastic.co/integrations/ti_opencti)
+  * NOTE: This field set can be greatly simplified by using existing ECS common fields as well as modeling the observable field set more closely with the indicator object from the threat field set.
+* [STIX 2.1 Cyber observable objects](https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_mlbmudhl16lr)
+
+### RFC Pull Requests
+
+<!-- An RFC should link to the PRs for each of it stage advancements. -->
+
+* Stage 0: https://github.com/elastic/ecs/pull/2311
+
+<!--
+* Stage 1: https://github.com/elastic/ecs/pull/NNN
+...
+-->
diff --git a/rfcs/text/0000/observable.yml b/rfcs/text/0000/observable.yml
new file mode 100644
index 0000000000..f8439da517
--- /dev/null
+++ b/rfcs/text/0000/observable.yml
@@ -0,0 +1,143 @@
+- name: observable
+  title: Observable
+  short: Fields describing an observable.
+  description: >-
+    Observable fields capture details about a cyber observable. Cyber observables are
+    raw artifacts that can be observed in network traffic, system logs, or other data sources.
+  
+  fields:
+
+    - name: description
+      level: custom
+      type: text
+      short: Description of the observable.
+      description: >-
+        A description of the observable.
+      example: IP x.x.x.x was observed in investigation y.
+
+    - name: domain
+      level: custom
+      type: keyword
+      short: Domain name of the observable.
+      description: >-
+        Identifies an observable as a domain name. Only filled in when value is a domain.
+      example: elastic.co
+
+    - name: email.address
+      level: custom
+      type: keyword
+      short: Email address of the observable.
+      description: >-
+        Identifies an observable as an email address. Only filled in when value is an email address.
+      example: phish@example.com
+
+    - name: first_seen
+      level: custom
+      type: date
+      short: First time the observable was seen.
+      description: >-
+        Only filled in when value is a domain.
+      example: 2019-01-01T00:00:00.000Z
+
+    - name: id
+      level: custom
+      type: keyword
+      short: Unique identifier of the observable.
+      description: >-
+        The unique identifier of the observable typically in STIX serialization format.
+      example: ipv4-addr--cbd67181-b9f8-595b-8bc3-3971e34fa1cc
+
+    - name: ip
+      level: custom
+      type: ip
+      short: IP address of the observable.
+      description: >-
+        Identifies an observable as an IP address. Only filled in when value is an IP address.
+      example: 1.1.1.1
+
+    - name: last_seen
+      level: custom
+      type: date
+      short: Last time the observable was seen.
+      description: >-
+        Only filled in when value is a domain.
+      example: 2019-01-01T00:00:00.000Z
+
+    - name: modified_at
+      level: custom
+      type: date
+      short: Last time the observable was modified.
+      description: >-
+        Only filled in when value is a domain.
+      example: 2019-01-01T00:00:00.000Z
+
+    - name: name
+      level: custom
+      type: keyword
+      short: observable display name.
+      description: >-
+        The display name observable in an UI friendly format
+
+        URL, IP address, email address, registry key, port number, hash value,
+        or other relevant name can serve as the display name.
+      example: 5.2.75.227
+
+    - name: port
+      level: custom
+      type: long
+      short: Port number of the observable.
+      description: >-
+        Identifies an observable as a port number (irrespective of direction).
+      example: 443
+
+    - name: provider
+      level: custom
+      type: keyword
+      short: Provider of the observable.
+      description: >-
+        The name of the observable's provider.
+      example: sensor
+      normalize:
+        - array
+
+    - name: reference
+      level: custom
+      type: keyword
+      short: Reference to the observable.
+      description: >-
+        Reference URL linking to additional information about this observable.
+      example: https://system.example.com/observable/0001234
+
+    - name: spec_version
+      level: custom
+      type: keyword
+      short: STIX 2.x specification version.
+      description: >-
+        STIX 2.x specification version.
+      example: 2.1
+
+    - name: type
+      level: custom
+      type: keyword
+      short: observable type.
+      description: >
+        Type of observable as represented by Cyber Observable in STIX 2.0.
+      expected_values:
+        - autonomous-system
+        - artifact
+        - directory
+        - domain-name
+        - email-addr
+        - file
+        - ipv4-addr
+        - ipv6-addr
+        - mac-addr
+        - mutex
+        - port
+        - process
+        - software
+        - url
+        - user-account
+        - windows-registry-key
+        - x509-certificate
+      example: ipv4-addr