user10279: I have a MacBook Pro running OS X Yosemite (10.10.3). I connected my Arduino UNO R3 to my computer for the first time after the Yosemite upgrade - it worked fine before this!
When I opened the Arduino IDE I selected Tools > Board > "Arduino UNO", but when I try to choose a Serial Port the only options are:
/dev/tty.Bluetooth-Incoming-Port
/dev/cu.Bluetooth-Incoming-Port
/dev/tty.Bluetooth-Modem
/dev/cu.Bluetooth-Modem

I have followed several tutorials and threads on how to 'fix' this issue, all to no avail:
I've installed the latest version of the FTDI drivers (even though, from what I recall the UNO doesn't even need them): FTDIUSBSerialDriver_v2_3.dmg
Downgraded to a prev. version of the FTDI driver hoping that would clear it up: /Volumes/FTDIUSBSerialDriver_v2_2_18
I followed a tutorial of how to remove the existing Apple drivers and removed the kext files, etc... 
Tried connecting arduino to both USB ports.
Tried various cables, including the one that a I used before the Yosemite upgrade.
Tried installing updated Silabs drivers:
Arduino compatible's serial port not showing Mac OSX
Walked through the entire Arduino Mac OSX guide:
http://www.arduino.cc/en/guide/macOSX
After looking into the system info of my Macbook Pro, I can see the USB Controller is Broadcom based, in case that helps. I searched for Broadcom USB drivers but got hits for Silabs one instead.
Under my Tools > Port menu.. I can see these options:

clicking the Serial Ports option doesn't do anything.
Running ls -1 /dev/tty.* or ls -l /dev/tty.usb* from terminal gives me:
/dev/tty.Bluetooth-Incoming-Port
/dev/tty.Bluetooth-Modem

The Board does NOT show up under system networking (as it has for others), so it's not recognized as an incorrect device.
I'm at a complete loss. The board powers up... but I cannot connect to it.
SIDE NOTE: This is a legit Uno R3, not a clone.

user13984: Check this video https://www.youtube.com/watch?v=0zuRukW7o0A

Reboot and press CMD+R immediately after reboot to enter in Recovery Mode
Open Terminal from Recovery mode
Run the command csrutil enable --without kext
Reboot
Install driver


user29619: I have an osepp r3, seemingly an accurate clone. Computer is Mac os10.10.5. 
A lot of sites claimed that the mac osx.* does not require FTDI drivers, but.....
After an awkward, google searching beginning, where the board only accepted a new sketch after being physically unplugged and replugged, I downloaded the latest FTDI driver, installed, and RESTARTED the mac. Now, joy and peace reigns. No side-effects with other mac functions, thankfully. Hope this helps. 

user9826: This exact same thing happen to me on my mac running the same operating system. I had to restart this system a few times to get it to work. I restarted it with the arduino plugged in; and that worked rather than my previous attempts when i rebooted then plugged in.

user651: Yosemite 10.9 (and OS X 10.10 and newer) requires a signed USB driver kext (kernel extension).  You can find one on the FTDI web site here: http://www.ftdichip.com/Drivers/VCP.htm
Use version 2.3 for 64-bit OS X 10.9 or later.  Install and reboot.
Plug in your Arduino, and the Terminal command:

/usr/sbin/kextstat | grep FTDI

will tell you if the FTDI VCP driver actually loaded.
Also a /dev/tty.usbserial-xxxxxxxx entry should appear in your /dev directory.
If not, the Mac USB port isn't talking to your Arduino.  So it's no use trying the Arduino IDE application.
Also make sure your USB cable isn't for power only, but fully connected.

user13695: This site fixed the problem for me:
http://kiguino.moos.io/2014/12/31/how-to-use-arduino-nano-mini-pro-with-CH340G-on-mac-osx-yosemite.html
...somebody else has made an alternative to the ftdi drivers, and this website show you how to install them correctly.

user16666: This fixed the problem for me:
http://blog.sengotta.net/signed-mac-os-driver-for-winchiphead-ch340-serial-bridge/
... and the direct link to download.
EDIT: I have one of the cheap clones with a CH340 USB chip. So this might not solve your problem, but could be beneficial to others.

user10847: The cable that shipped with my Arduino Uno worked for power but not data transmission so the /dev/tty.usbmodem was not showing up in the Tools --> Port menu. After I switched to a different cable, the /dev/tty.usbmodem port showed up and it worked beautifully. 

user14475: Probably, you have Chinese Uno analog which works on CH340 USB-to-serial chip, so you need to install driver for it.
Steps to fix:

Install the CH340 driver
Run the command in Terminal: sudo nvram boot-args="kext-dev-mode=1" (disable kext signing introduced in Mac OS X 10.9 Yosemite)
Reboot

Also you're right according to Uno and FDTI:

Differences with other boards
The Uno differs from all preceding boards in that it does not use the FTDI USB-to-serial driver chip. Instead, it features the Atmega16U2 (Atmega8U2 up to version R2) programmed as a USB-to-serial converter.


10279: <p>I have a MacBook Pro running OS X Yosemite (10.10.3). I connected my Arduino UNO R3 to my computer for the first time after the Yosemite upgrade - it worked fine before this!</p>

<p>When I opened the Arduino IDE I selected Tools > Board > "Arduino UNO", but when I try to choose a Serial Port the only options are:</p>

<pre><code>/dev/tty.Bluetooth-Incoming-Port
/dev/cu.Bluetooth-Incoming-Port
/dev/tty.Bluetooth-Modem
/dev/cu.Bluetooth-Modem
</code></pre>

<p>I have followed several tutorials and threads on how to 'fix' this issue, all to no avail:</p>

<p>I've installed the latest version of the FTDI drivers (even though, from what I recall the UNO doesn't even need them): FTDIUSBSerialDriver_v2_3.dmg</p>

<p>Downgraded to a prev. version of the FTDI driver hoping that would clear it up: /Volumes/FTDIUSBSerialDriver_v2_2_18</p>

<p>I followed a tutorial of how to remove the existing Apple drivers and removed the kext files, etc... </p>

<p>Tried connecting arduino to both USB ports.</p>

<p>Tried various cables, including the one that a I used before the Yosemite upgrade.</p>

<p>Tried installing updated Silabs drivers:
<a href="https://arduino.stackexchange.com/questions/3324/arduino-compatibles-serial-port-not-showing-mac-osx/3328#3328">Arduino compatible&#39;s serial port not showing Mac OSX</a></p>

<p>Walked through the entire Arduino Mac OSX guide:
<a href="http://www.arduino.cc/en/guide/macOSX" rel="noreferrer">http://www.arduino.cc/en/guide/macOSX</a></p>

<p>After looking into the system info of my Macbook Pro, I can see the USB Controller is Broadcom based, in case that helps. I searched for Broadcom USB drivers but got hits for Silabs one instead.</p>

<p>Under my Tools > Port menu.. I can see these options:
<img src="https://i.stack.imgur.com/MOvDD.png" alt="enter image description here">
clicking the Serial Ports option doesn't do anything.</p>

<p>Running <code>ls -1 /dev/tty.*</code> or <code>ls -l /dev/tty.usb*</code> from terminal gives me:</p>

<pre><code>/dev/tty.Bluetooth-Incoming-Port
/dev/tty.Bluetooth-Modem
</code></pre>

<p>The Board does NOT show up under system networking (as it has for others), so it's not recognized as an incorrect device.</p>

<p>I'm at a complete loss. The board powers up... but I cannot connect to it.</p>

<p>SIDE NOTE: This is a legit Uno R3, not a clone.</p>
 13984: <p>Check this video <a href="https://www.youtube.com/watch?v=0zuRukW7o0A" rel="nofollow">https://www.youtube.com/watch?v=0zuRukW7o0A</a></p>

<ul>
<li>Reboot and press CMD+R immediately after reboot to enter in Recovery Mode</li>
<li>Open Terminal from Recovery mode</li>
<li>Run the command csrutil enable --without kext</li>
<li>Reboot</li>
<li>Install driver</li>
</ul>
 29619: <p>I have an osepp r3, seemingly an accurate clone. Computer is Mac os10.10.5. </p>

<p>A lot of sites claimed that the mac osx.* does not require FTDI drivers, but.....</p>

<p>After an awkward, google searching beginning, where the board only accepted a new sketch after being physically unplugged and replugged, I downloaded the latest FTDI driver, installed, and RESTARTED the mac. Now, joy and peace reigns. No side-effects with other mac functions, thankfully. Hope this helps. </p>
 9826: <p>This exact same thing happen to me on my mac running the same operating system. I had to restart this system a few times to get it to work. I restarted it with the arduino plugged in; and that worked rather than my previous attempts when i rebooted then plugged in.</p>
 651: <p>Yosemite 10.9 (and OS X 10.10 and newer) requires a signed USB driver kext (kernel extension).  You can find one on the FTDI web site here: <a href="http://www.ftdichip.com/Drivers/VCP.htm" rel="noreferrer">http://www.ftdichip.com/Drivers/VCP.htm</a><br>
Use version 2.3 for 64-bit OS X 10.9 or later.  Install and reboot.</p>

<p>Plug in your Arduino, and the Terminal command:</p>

<blockquote>
  <p>/usr/sbin/kextstat | grep FTDI</p>
</blockquote>

<p>will tell you if the FTDI VCP driver actually loaded.</p>

<p>Also a /dev/tty.usbserial-xxxxxxxx entry should appear in your /dev directory.</p>

<p>If not, the Mac USB port isn't talking to your Arduino.  So it's no use trying the Arduino IDE application.</p>

<p>Also make sure your USB cable isn't for power only, but fully connected.</p>
 13695: <p>This site fixed the problem for me:</p>

<p><a href="http://kiguino.moos.io/2014/12/31/how-to-use-arduino-nano-mini-pro-with-CH340G-on-mac-osx-yosemite.html" rel="noreferrer">http://kiguino.moos.io/2014/12/31/how-to-use-arduino-nano-mini-pro-with-CH340G-on-mac-osx-yosemite.html</a></p>

<p>...somebody else has made an alternative to the ftdi drivers, and this website show you how to install them correctly.</p>
 16666: <p>This fixed the problem for me:</p>

<p><a href="http://blog.sengotta.net/signed-mac-os-driver-for-winchiphead-ch340-serial-bridge/" rel="noreferrer">http://blog.sengotta.net/signed-mac-os-driver-for-winchiphead-ch340-serial-bridge/</a></p>

<p>... and the <a href="http://blog.sengotta.net/wp-content/uploads/2015/11/CH34x_Install.zip" rel="noreferrer">direct link</a> to download.</p>

<p><strong>EDIT</strong>: I have one of the cheap clones with a CH340 USB chip. So this might not solve <em>your</em> problem, but could be beneficial to others.</p>
 10847: <p>The cable that shipped with my Arduino Uno worked for power but not data transmission so the /dev/tty.usbmodem was not showing up in the Tools --> Port menu. After I switched to a different cable, the /dev/tty.usbmodem port showed up and it worked beautifully. </p>
 14475: <p>Probably, you have Chinese Uno analog which works on <strong>CH340</strong> USB-to-serial chip, so you need to install driver for it.</p>

<p>Steps to fix:</p>

<ol>
<li>Install the <a href="http://www.wch.cn/download/CH341SER_MAC_ZIP.html">CH340 driver</a></li>
<li>Run the command in Terminal: <code>sudo nvram boot-args="kext-dev-mode=1"</code> (disable kext signing introduced in Mac OS X 10.9 Yosemite)</li>
<li>Reboot</li>
</ol>

<p>Also you're right <a href="https://www.arduino.cc/en/Main/ArduinoBoardUno">according to Uno and FDTI</a>:</p>

<blockquote>
  <p><strong>Differences with other boards</strong></p>
  
  <p>The Uno differs from all preceding boards in that it <strong>does not</strong> use the FTDI USB-to-serial driver chip. Instead, it features the Atmega16U2 (Atmega8U2 up to version R2) programmed as a USB-to-serial converter.</p>
</blockquote>
