diff --git a/.github/cspell.json b/.github/cspell.json
index 5bedef4b..41226b2a 100644
--- a/.github/cspell.json
+++ b/.github/cspell.json
@@ -31,6 +31,11 @@
         "PCKID",
         "pccs",
         "pckcache",
-        "sysfs"
+        "sysfs",
+        "UEFI",
+        "ACPI",
+        "MRTD",
+        "CCEL",
+        "Bootloader"
     ]
 }
\ No newline at end of file
diff --git a/README.md b/README.md
index 25c1d94c..2f17e24f 100644
--- a/README.md
+++ b/README.md
@@ -1,9 +1,36 @@
 # CC Trusted API
 
-The project helps to access and process the trusted primitives (measurement, eventlog,
-quote) in the confidential computing environment. It supports multiple language flavors.
-
-It also provides backend tools, IMA templates, services to produce the diverse TCBs
-according to deployment.
+CC Trusted API helps the diverse applications to access and process the trust states
+which was represented by integrity measurement, event record, report/quote in the confidential
+computing environment.
 
 ![](docs/cc-trusted-api-overview.png)
+
+## TCB Measurement
+
+The diverse application in confidential computing could be firmware or monolithic application
+in Confidential VM(CVM), micro service or macro service on Kubernetes. Although
+different type application might get the trust states measured in different Trusted
+Computing Base (TCB), but the definition and structure of integrity measurement,
+event record follows [TCG PC Client Platform Firmware Profile Specification](https://trustedcomputinggroup.org/wp-content/uploads/TCG_PCClient_PFP_r1p05_v23_pub.pdf)
+
+![](docs/cc-trusted-api-usage.png)
+| TCB | Measured By | Specification |
+| --- | -------- | ------------- |
+| TEE | Vendor Secure Module like Intel TDX module, SEV secure processor | Vendor Specification like [Intel TDX Module Specification](https://cdrdv2-public.intel.com/733575/intel-tdx-module-1.5-base-spec-348549002.pdf) |
+| Firmware | [EFI_CC_MEASUREMENT_PROTOCOL](https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Protocol/CcMeasurement.h) | [UEFI Specification 2.10](https://uefi.org/specs/UEFI/2.10/) |
+| Boot Loader | [EFI_CC_MEASUREMENT_PROTOCOL](https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Protocol/CcMeasurement.h) | Grub2/Shim |
+| OS | Integrity Measurement Architecture (IMA)) | [Specification]((https://sourceforge.net/p/linux-ima/wiki/Home/)) |
+| Cloud Native | Confidential Cloud Native Primitives (CCNP) | [Repository](https://github.com/intel/confidential-cloud-native-primitives) |
+
+## Trusted Foundation
+
+Normally Trusted Platform Module(TPM) provides root of trust for PC client platform.
+In confidential computing environment, vTPM (virtual TPM) might be provided different
+vendor or CSP, which root of trust should be hardened by vendor secure module. Some
+vendor also provided simplified solution:
+
+|    | Intel | vTPM |
+| --- | --- | --- |
+| Integrity Measurement Register | RTMR/MRTD | PCR |
+| Event Log ACPI table | CCEL | TPM2 |
diff --git a/docs/cc-trusted-api-usage.png b/docs/cc-trusted-api-usage.png
new file mode 100644
index 00000000..b500fdf5
Binary files /dev/null and b/docs/cc-trusted-api-usage.png differ