┌──────────────────────────┐
      │       Interactive?       │──────────▶  No
      └──────────────────────────┘
                    │                           │
                    ▼                           │
                                                │
                   Yes                          ▼
                                     ┌────────────────────┐
                    │                │   --login Flag?    │───────▶  No
                    ▼                └────────────────────┘
      ┌──────────────────────────┐              │                     │
      │       Login Shell?       │──┐    ┌──────┘                     ▼
      └──────────────────────────┘  │    ▼                    .───────────────.
                    │               │                        (    $BASH_ENV    )
                    ▼               └─▶ Yes  ───┐             `───────────────'
                                                │
                    No                          ▼
                                     ┌────────────────────┐
                    │                │ --noprofile Flag?  │─────────▶  No
                    ▼                └────────────────────┘
      ┌──────────────────────────┐              │                       │
      │  --rcfile <file> Flag?   │────▶ Yes  ─┐ │                       │
      └──────────────────────────┘            │ └──────────┐            │
                    │                         │            │            │
                    ▼                         ▼            ▼            │
                                      .───────────────.                 │
                    No               (     <file>      )  No            │
                                      `───────────────'                 │
                    │                                      │            │
                    ▼                                      │            ▼
      ┌───────────────────────────┐                        │    .───────────────.
      │       --norc Flag?        │───▶ Yes  ──┬───────────┘   (  /etc/profile   )
      └───────────────────────────┘            │                `───────────────'
                    │                          │                        │
                    ▼                          ▼                        │
                                    ╔════════════════════╗              ▼
                   No               ║  No File Loaded!   ║ /────────────────────────\\
                                    ╚════════════════════╝ │ First Of:              │
                    │                                      │  - $HOME/.bash_profile │
                    ▼                                      │  - $HOME/.bash_login   │
        .───────────────────────.                          │  - $HOME/.profile      │
       (    /etc/bash/bash.rc    )                         \\────────────────────────/
        `───────────────────────'                                       │
                    │
                    │                .───────────────────.              │
                    └──────────────▶(    $HOME/.bashrc    )◀ ─ ─ ─ ─ ─ ─   May Include
                                     `───────────────────'

Invoked as an interactive login shell, or with --login When Bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and executes commands from the file /etc/profile, if that file exists. After reading that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that exists and is readable. The --noprofile option may be used when the shell is started to inhibit this behavior.

When a login shell exits, Bash reads and executes commands from the file ~/.bash_logout, if it exists.

Invoked as an interactive non-login shell When an interactive shell that is not a login shell is started, Bash reads and executes commands from ~/.bashrc, if that file exists. This may be inhibited by using the --norc option. The --rcfile file option will force Bash to read and execute commands from file instead of ~/.bashrc.

By default, Terminal starts the shell via /usr/bin/login, which makes the shell a login shell. On every platform (not just Mac OS X) bash does not use .bashrc for login shells (only /etc/profile and the first of .bash_profile, .bash_login, .profile that exists and is readable). This is why “put source ~/.bashrc in your .bash_profile” is standard advice.

So typically (or sooner or later), what you will encounter are non-login shells. So this case is what you should write your config files for. This means putting most of your stuff in ~/.bashrc, having exactly one of ~/.bash_profile, ~/.bash_login, and ~/.profile, and sourcing ~/.bashrc from it.

On startup, bash executes any script labeled A in the table below, followed by the first script B it finds. On exit, it executes any script labeled C.

Interactive login Interactive non-login Non-interactive Remote shell
/etc/profile A
/etc/bash.bashrc A
~/.bashrc B A
~/.bash_profile B1
~/.bash_login B2
~/.profile B3
BASH_ENV A
~/.bash_logout C
Author is lost 
The author of the scheme is lost :(
If you know who the author is, please let me know.