Polite Ways to Say "Hello" in Japanese

The standard polite hello in Japanese is こんにちは (konnichiwa), used from late morning through the afternoon. Japanese also has polite greetings tied to the time of day and to whether you are meeting someone for the first time, and choosing the right one is what makes you sound courteous.

The most common way

konnichiwa

A neutral, polite hello — the default daytime greeting for anyone you are not close to.

How to say it: The last syllable is written は but pronounced "wa"; keep the pitch flat and don't stress the "ni".

Other ways to say it

polite, morning
ohayō gozaimasu
A respectful good morning, used until roughly 10 or 11 a.m.
When to use it: Say it to colleagues, teachers, customers or neighbours first thing in the day; the short おはよう without ございます is only for friends and family.
polite, evening
konbanwa
A neutral, polite good evening, used after dark.
When to use it: Use it from early evening onward with anyone, including strangers and people senior to you.
formal, first meeting
hajimemashite
How do you do — the set phrase for meeting someone for the very first time.
When to use it: Say it once, at the start of a self-introduction, before giving your name; it is polite with everyone.
business, very formal
osewa ni natte orimasu
Literally "you are always in my debt" — a humble, fixed business greeting meaning hello and thank you for your continued support.
When to use it: Open phone calls, emails and meetings with clients, suppliers or other companies; it sounds odd between friends.
refined, slightly old-fashioned
gokigen'yō
A gracious, rather elegant good day, also used as a goodbye; warmer and softer than it sounds.
When to use it: Say it to people much older than you, at formal or ceremonial occasions, or in letters; younger speakers rarely use it.

In a conversation

A
。。
Osewa ni natte orimasu. Maruyama Shōji no Tanaka to mōshimasu.
Hello, and thank you for your continued business. My name is Tanaka of Maruyama Trading.
B
、。
Kochira koso, osewa ni natte orimasu.
Likewise, thank you for your continued business.
A
、。
Honjitsu wa ojikan o itadaki, arigatō gozaimasu.
Thank you for making time for me today.

Common mistakes

~~こんにちは~~ → おはようございます
こんにちは sounds wrong first thing in the morning, because Japanese greetings are tied to the time of day.
~~はじめまして~~ → お久しぶりです
はじめまして only works at a genuine first meeting; for people you already know, use お久しぶりです (ohisashiburi desu, "long time no see").
~~おはよう~~ → おはようございます
Dropping ございます is fine with friends but can sound too casual with a boss, teacher or customer.