diff --git a/pkg/apis/certificates/types.go b/pkg/apis/certificates/types.go
index b616c000113..a2a15a68649 100644
--- a/pkg/apis/certificates/types.go
+++ b/pkg/apis/certificates/types.go
@@ -45,10 +45,27 @@ type CertificateSigningRequestSpec struct {
 	// Base64-encoded PKCS#10 CSR data
 	Request []byte
 
-	// Requested signer for the request. It is a qualified name in the form:
-	// `scope-hostname.io/name`.
-	// Distribution of trust for signers happens out of band.
-	// You can select on this field using `spec.signerName`.
+	// signerName indicates the requested signer, and is a qualified name.
+	//
+	// List/watch requests for CertificateSigningRequests can filter on this field using a "spec.signerName=NAME" fieldSelector.
+	//
+	// Well-known Kubernetes signers are:
+	//  1. "kubernetes.io/kube-apiserver-client": issues client certificates that can be used to authenticate to kube-apiserver.
+	//   Requests for this signer are never auto-approved by kube-controller-manager, can be issued by the "csrsigning" controller in kube-controller-manager.
+	//  2. "kubernetes.io/kube-apiserver-client-kubelet": issues client certificates that kubelets use to authenticate to kube-apiserver.
+	//   Requests for this signer can be auto-approved by the "csrapproving" controller in kube-controller-manager, and can be issued by the "csrsigning" controller in kube-controller-manager.
+	//  3. "kubernetes.io/kubelet-serving" issues serving certificates that kubelets use to serve TLS endpoints, which kube-apiserver can connect to securely.
+	//   Requests for this signer are never auto-approved by kube-controller-manager, and can be issued by the "csrsigning" controller in kube-controller-manager.
+	//
+	// More details are available at https://k8s.io/docs/reference/access-authn-authz/certificate-signing-requests/#kubernetes-signers
+	//
+	// Custom signerNames can also be specified. The signer defines:
+	//  1. Trust distribution: how trust (CA bundles) are distributed.
+	//  2. Permitted subjects: and behavior when a disallowed subject is requested.
+	//  3. Required, permitted, or forbidden x509 extensions in the request (including whether subjectAltNames are allowed, which types, restrictions on allowed values) and behavior when a disallowed extension is requested.
+	//  4. Required, permitted, or forbidden key usages / extended key usages.
+	//  5. Expiration/certificate lifetime: whether it is fixed by the signer, configurable by the admin.
+	//  6. Whether or not requests for CA certificates are allowed.
 	SignerName string
 
 	// usages specifies a set of usage contexts the key will be