My OSX/macOS tmux configuration, tested on 10.11.x

.tmux.conf

#allow mousing
set -g mouse-utf8 on
set -g mouse on

# Return pre-2.1 mousing behaviour
# https://github.com/tmux/tmux/issues/145
bind -n WheelUpPane if-shell -F -t = "#{mouse_any_flag}" "send-keys -M" "if -Ft= '#{pane_in_mode}' 'send-keys -M' 'select-pane -t=; copy-mode -e; send-keys -M'"
bind -n WheelDownPane select-pane -t= \; send-keys -M

# Use vim keybindings in copy mode
setw -g mode-keys vi

# Setup 'v' to begin selection as in Vim
bind-key -t vi-copy v begin-selection
bind-key -t vi-copy y copy-pipe "pbcopy"

# # Update default binding of `Enter` to also use copy-pipe
unbind -t vi-copy Enter
bind-key -t vi-copy Enter copy-pipe "pbcopy"