The core of Azure Functions is its Azure runtime. The precursor to Azure Functions was Azure WebJobs. The code for Azure WebJobs also forms the core for Azure Functions. There are additional features and extensions added to Azure WebJobs to create Azure Functions. The Functions runtime is the magic behind making Functions work. Azure Functions are hosted within Azure App Service. Azure App Service loads the Azure runtime and either waits for an external event to occurs or for any HTTP requests. On arrival of a request or the occurrence of a trigger, App Service loads the incoming payload, reads the Function's function.json file to find the Function's bindings and trigger, maps the incoming data to incoming parameters, and invokes the Function with parameter values. Once the Function completes its execution, the value is again passed back to the Azure Functions runtime by way of an outgoing parameter defined as a binding in the function.json file. The Function runtime returns the values to the caller. The Azure Functions runtime acts as the glue that enables the entire performance of Functions.