Zero Trust is a security posture where no user, device, or network location is automatically trusted. Every access request is verified, regardless of where it originates. This replaces the older "trust the inside, distrust the outside" model that assumed your office network was safe. In practice, Zero Trust means strong authentication on every login, continuous device-health checks, and granular permissions based on what a user actually needs.
Why the old model failed
Traditional network security assumed a hard perimeter: a firewall around the office network kept attackers out, and anyone inside was trusted. Three things broke that model. Cloud SaaS (your data is no longer on your network). Remote work (your employees are no longer on your network). And lateral movement (once an attacker compromises a single device on your network, they have everything). The "inside" stopped being safer than the "outside."
Core principles of Zero Trust
Verify explicitly: authenticate every request using identity, device state, and context. Use least privilege: users get only the access they need, only for as long as they need it. Assume breach: design as if an attacker is already inside. Segment the network so a single compromised device cannot reach everything.
What Zero Trust looks like for an SMB
You do not need a million-dollar identity platform to start. Practical first steps: enforce MFA on every account (especially Microsoft 365 / Google Workspace administrators), turn on conditional access policies that block logins from unfamiliar locations or unmanaged devices, audit and trim Microsoft 365 / SharePoint sharing permissions, and deploy endpoint protection that reports device posture back to your identity provider. These four moves get an SMB 80% of the way to a meaningful Zero Trust posture for a fraction of the enterprise cost.