Letter writing remains a fundamental aspect of effective communication, enabling individuals to convey messages in a structured and lasting format. The primary distinction lies in the letter's purpose and the relationship between the sender and receiver, which dictates its tone and conventions.

Formal Letters are characterized by their professional, objective, and respectful tone. They are typically written for official purposes, such as applying for a job, making a complaint, placing an order, requesting information, or communicating with institutions and businesses. The structure of a formal letter is rigid and must be adhered to for clarity and professionalism. It always begins with the sender's address, usually placed at the top right or left, followed by the date. Below this, on the left side, comes the receiver's full address. The salutation is formal and respectful, such as "Dear Sir/Madam," or "Dear Mr./Ms. [Surname]." A concise subject line is crucial, immediately informing the recipient of the letter's purpose.

The body of the letter typically comprises three parts: an introduction that clearly states the reason for writing; the main content, where all relevant details, arguments, or requests are clearly articulated in a logical and organized manner; and a conclusion that summarizes the main points and specifies any expected action or next steps.

The language used must be precise, grammatically correct, and free of contractions, slang, or overly emotional expressions. The letter concludes with a formal complimentary close, such as "Yours faithfully" (if the recipient's name is unknown) or "Yours sincerely" (if the recipient's name is known), followed by the sender's handwritten signature and their full name in block letters, often with their designation.

Understanding specific scenarios is key: official letters to government bodies require strict adherence to protocol, business letters focus on transactions and clarity, application letters highlight qualifications relevant to a role, and complaint letters must clearly outline the problem, provide evidence, and propose a resolution.

Informal Letters, in contrast, are personal communications exchanged between friends, family members, or close acquaintances. Their primary purpose is to share personal news, express feelings, or maintain social connections.

The structure is less rigid than formal letters but still follows a general pattern. The sender's address and date are usually placed at the top right or left. The salutation is informal and affectionate, like "Dear [First Name]," or "Hi [Name]." The body of an informal letter is conversational and can vary widely in content and length.

The tone is warm, friendly, and reflective of the relationship between the correspondents, allowing for the use of contractions, idiomatic expressions, and even slang, if appropriate. The letter concludes with a warm closing remark and an informal complimentary close such as "Love," "Best regards," or "Cheers," followed by the sender's first name or nickname.