To the average person in tech, Human-Computer Interaction (HCI) might just sound like a fancy way of saying making a product that feels good to use. And while yes – it seems like a straightforward practice – this is only one small fraction of a much larger idea, and a whole lot harder to implement. HCI is about understanding how humans think, act, and adapt – and being able to design technology that fits those patterns. It isn’t just for UX designers or people working in consumer tech; HCI serves as the foundation for everything we build. Learning HCI means learning to work with human empathy in mind and connect the things we develop with the experiences we’re truly building.

What is HCI?

An interface is the medium (hardware or software) through which a user communicates with a system. Interaction is the process of how the user accomplishes goals through that interface. HCI is the practice of designing and implementing interfaces, and the distinction here is that HCI isn’t just about visuals, but behaviour.

Every HCI decision ladders up to one objective: usability – how effectively and efficiently a user can achieve their goals. Good usability involves some of the following:

• Discoverability: Users can easily find what they need without a manual
• Reliability and trust: Systems function consistently
• Error tolerance: People make mistakes, and good products forgive them
• Learnability: The more the user uses a product, the easier it gets

You’ll probably hear the word trade-off in tech a lot, and HCI makes it explicit why they exist: there is no such thing as a universal user. People differ in culture, ability, perception, and experience. Designing for everyone means making informed compromises, or sometimes building multiple solutions for different needs.

Principles, Guidelines, and Theories

HCI operates at three levels:

1. Principles: Broad, experience-based rules. Although they often need more clarification, they are widely applicable
2. Guidelines: Context-specific best practices. They are specific to something, whether it be a company, a situation, etc
3. Theories: Theories are scientifically tested models that ground HCI in data, although they may not be as practical

Principles

Know the User

Every interface starts with an understanding of who it’s for — not in demographics, but in mental models. HCI encourages designers and builders to consider factors like age, ability, education, motivation, goals, and experience level. A common way to categorize users is as follows: