Introduction to AL

Learn what the Application Language is, how it fits into Business Central, and the core concepts every BC developer needs to know.

25 minBeginner

Learning Objectives

Understand what AL (Application Language) is and its role in BC
Learn about AL object types (Tables, Pages, Codeunits, Reports)
Understand triggers, events, and procedures
Know the difference between base application and extensions

What is Business Central?

Microsoft Dynamics 365 Business Central is a comprehensive cloud ERP solution for small and medium-sized businesses. It automates and streamlines business processes across finance, manufacturing, sales, supply chain, projects, and services.

Business Central provides a complete view of your organization — connecting sales, service, finance, and operations teams to help you adapt faster and deliver results.

Cloud-First ERP

Business Central runs primarily in the cloud (SaaS), but on-premises deployments are also supported. Extension development works the same way regardless of deployment model.

What is AL?

The Application Language (AL) is the programming language used to write code for Microsoft Dynamics 365 Business Central. With AL, you can:

Manipulate data in the BC database
Create new business logic and UI
Subscribe to events in the base application
Connect to external web services
Build AppSource-ready extensions

AL is written in Visual Studio Code with the AL Language extension. It replaced C/AL (the old NAV development language) and is the only supported language for BC extension development.

AL Object Types

Every BC application is built from AL objects. The main types you'll work with:

Object	Purpose
Table	Defines data structure and business logic for data
Page	User interface for viewing and editing data
Codeunit	Business logic not tied to a specific table
Report	Formatted output and data processing
Query	Read-only data access for reporting
XmlPort	Import/export data in XML or text formats
Enum	Fixed set of options (replaces legacy Option type)

Triggers and Events

In AL, objects have triggers — procedures that run automatically when specific events occur. Trigger names always start with On:

CustomerTable.Table.al

table 50100 "Customer Bonus"
{
    fields
    {
        field(1; "Customer No."; Code[20]) { }
        field(2; "Bonus Amount"; Decimal) { }
    }

    trigger OnInsert()
    begin
        ValidateBonus();
    end;

    local procedure ValidateBonus()
    begin
        if "Bonus Amount" < 0 then
            Error('Bonus amount cannot be negative.');
    end;
}

You can also write event subscribers to react to events in the base application without modifying Microsoft code:

SalesEvents.Codeunit.al

codeunit 50101 "Sales Event Subscriber"
{
    [EventSubscriber(ObjectType::Table, Database::"Sales Header", 'OnAfterInsertEvent', '', false, false)]
    local procedure OnAfterSalesHeaderInsert(var Rec: Record "Sales Header")
    begin
        // Custom logic after a sales order is created
    end;
}

Variables and Data Types

Like other programming languages, AL supports variables for temporary data storage:

var
    CustomerNo: Code[20];
    TotalAmount: Decimal;
    IsProcessed: Boolean;
    ItemDescription: Text[100];

AL has intrinsic data types including Integer, Decimal, Boolean, Text, Code, Date, DateTime, GUID, and more.

Start Simple

Focus on understanding tables and pages first. Most BC development revolves around these two object types. Codeunits and events come naturally once you're comfortable with the basics.

Extensions vs. Base Application

Microsoft ships the base application — you cannot modify it directly. Instead, you build extensions that layer on top:

Per-tenant extensions (PTE) — Customizations for a single customer
AppSource apps — Published extensions available to all BC customers
Global extensions — Microsoft's own feature additions

Your AL code always lives in an extension project, keeping the base application upgrade-safe.

Next Steps

In the next lesson, we'll dive into AL syntax — comments, compound statements, regions, and the coding conventions used by professional BC developers.