diff --git a/CODE_OF_CONDUCT.md b/CODE_OF_CONDUCT.md
new file mode 100644
index 0000000..7fb86f2
--- /dev/null
+++ b/CODE_OF_CONDUCT.md
@@ -0,0 +1 @@
+Please approach others with respect. That is everything.
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
new file mode 100644
index 0000000..35dedec
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1,11 @@
+## Contributing as a Developer
+- When creating a bug report: Please follow the template and provide detailed information.
+- When fixing a feature: Create a Pull Request (PR) with accompanying test code.
+- When adding a feature: First, propose the feature in an Issue.
+
+## Contributing Outside of Coding
+The following actions help boost my motivation:
+
+- Giving a GitHub Star
+- Promoting the application
+- Becoming a GitHub Sponsor
diff --git a/README.md b/README.md
index 7175071..9c47703 100644
--- a/README.md
+++ b/README.md
@@ -98,3 +98,18 @@ $ ./target/debug/cic --principal 1000000 --contribution 100000 --rate 10 --years
 ## License
 MIT
 
+## Contributing
+First off, thanks for taking the time to contribute! ❤️  See [CONTRIBUTING.md](./CONTRIBUTING.md) for more information.
+Contributions are not only related to development. For example, GitHub Star motivates me to develop!
+
+[![Star History Chart](https://api.star-history.com/svg?repos=nao1215/cic&type=Date)](https://star-history.com/#nao1215/cic&Date)
+
+## Side note
+
+The cic command is my first project in Rust. I am using it to learn how to write and structure projects in Rust.
+
+### Why did I choose the theme of compound interest?
+
+In Japan, the small amount investment tax exemption system (NISA) started gaining traction in 2024. I was fortunate enough to get involved in a NISA app at work.
+
+This led me to develop an interest in investments. So, it's not surprising that I chose compound interest as my theme.
diff --git a/SECURITY.md b/SECURITY.md
new file mode 100644
index 0000000..2b75a05
--- /dev/null
+++ b/SECURITY.md
@@ -0,0 +1,21 @@
+# Security Policy
+
+## Reporting a Vulnerability
+
+If you discover any security-related issues or vulnerabilities, please contact us at [n.chika156@gmail.com](mailto:n.chika156@gmail.com). We appreciate your responsible disclosure and will work with you to address the issue promptly.
+
+## Supported Versions
+
+We recommend using the latest release for the most up-to-date and secure experience. Security updates are provided for the latest stable version.
+
+## Security Policy
+
+- Security issues are treated with the highest priority.
+- We follow responsible disclosure practices.
+- Fixes for security vulnerabilities will be provided in a timely manner.
+
+## Acknowledgments
+
+We would like to thank the security researchers and contributors who responsibly report security issues and work with us to make our project more secure.
+
+Thank you for your help in making our project safe and secure for everyone.