ASN.1 is a binary language to describe structures through the definition of types. It scares a lot of developers, because it is non XML. At the base, it is a simple Tag Length Value (TLV) based format. ASN.1 is a lot used in cryptographic protocols, like signed and/or encrypted messages, communication between public key infrastructure (PKI) systems, SNMP, LDAP, X509v3 certificates … . When you develop application using cryptographic protocols and certificates, you’ll come in touch with ASN.1. So a developer needs a basis understanding of this binary format. The layman’s guide in the references is very good start to read.