- Combining al Qaeda's significant fighting capabilities with a stronger focus on the administrative capabilities that might permit it to hold ground, the Islamic State copied the latter from Hezbollah's model. Basically, Islamic State is a combined al Qaeda and Lebanese Hezbollah on steroids, destabilizing the region, dissolving borders/changing the political geography in the mid-east, and hardening political positions that make mid-east peace-building more remote by the day.
- That said, there are some assholes in the world that just need to be shot. There are hunters and there are victims. By your discipline, cunning, obedience and alertness, you will decide if you are a hunter or a victim. It’s really a hell of a lot of fun. You’re gonna have a blast out here!
- Addressing a gathering of 200 marines. 
- There is only one ‘retirement plan’ for terrorists.
- Speaking on the subject of combating insurgents. 
- For all the ‘4th Generation of War’ intellectuals running around today saying that the nature of war has fundamentally changed, the tactics are wholly new, etc., I must respectfully say, ‘Not really’: Alexander the Great would not be in the least bit perplexed by the enemy that we face right now in Iraq, and our leaders going into this fight do their troops a disservice by not studying — studying, vice just reading — the men who have gone before us. We have been fighting on this planet for 5,000 years and we should take advantage of their experience. ‘Winging it’ and filling body bags as we sort out what works reminds us of the moral dictates and the cost of competence in our profession.
- Nov. 20, 2003, Addressing the detractors of untested Marine tactics in Iraq. 
- You go into Afghanistan, you got guys who slap women around for five years because they didn't wear a veil. You know, guys like that ain't got no manhood left anyway. So it's a hell of a lot of fun to shoot them. Actually it's quite fun to fight them, you know. It's a hell of a hoot. It's fun to shoot some people. I'll be right up there with you. I like brawling.
- Panel discussion in San Diego, California (1 February 2005) as quoted in "General: It's 'fun to shoot some people'" CNN (4 February 2005)(For a more contextualized explanation of General Mattis' remarks, see this essay by one of the Marines who served under Mattis: "Breaking the Warrior Code" The American Spectator (February 11, 2005) by John R. Guardiano
- For decades, Saddam Hussein has tortured, imprisoned, raped and murdered the Iraqi people; invaded neighboring countries without provocation; and threatened the world with weapons of mass destruction. The time has come to end his reign of terror. On your young shoulders rest the hopes of mankind. When I give you the word, together we will cross the Line of Departure, close with those forces that choose to fight, and destroy them. Our fight is not with the Iraqi people, nor is it with members of the Iraqi army who choose to surrender. While we will move swiftly and aggressively against those who resist, we will treat all others with decency, demonstrating chivalry and soldierly compassion for people who have endured a lifetime under Saddam’s oppression. Chemical attack, treachery, and use of the innocent as human shields can be expected, as can other unethical tactics. Take it all in stride. Be the hunter, not the hunted: never allow your unit to be caught with its guard down. Use good judgment and act in best interests of our Nation. You are part of the world’s most feared and trusted force. Engage your brain before you engage your weapon. Share your courage with each other as we enter the uncertain terrain north of the Line of Departure. Keep faith in your comrades on your left and right and Marine Air overhead. Fight with a happy heart and strong spirit. For the mission’s sake, our country’s sake, and the sake of the men who carried the Division’s colors in the past battles-who fought for life and never lost their nerve-carry out your mission and keep your honor clean. Demonstrate to the world there is "No Better Friend, No Worse Enemy" than a U.S. Marine.
- Mattis' words in a message to the 1st Marine Division in March 2003, on the eve of the Iraq War, as quoted in "Eve of Battle Speech" in The Weekly Standard (1 March 2003); also quoted in War Stories: Operation Iraqi Freedom (2003) by Oliver North, p. 53
- Be polite, be professional, but have a plan to kill everybody you meet.
- One of the rules Maj. Gen. James Mattis gave his Marines to live by in Iraq, as quoted in Fiasco: The American Military Adventure in Iraq (2006) by Thomas E. Ricks; as excerpted in Armed Forces Journal (August 2006)
- I come in peace. I didn’t bring artillery. But I’m pleading with you, with tears in my eyes: If you fuck with me, I’ll kill you all.
- After the invasion of Iraq -and after sending his tanks and artillery home- Mattis sent this message to the Iraqi leaders in every area his men served in, as quoted in Fiasco: The American Military Adventure in Iraq (2006) by Thomas E. Ricks; as excerpted in Armed Forces Journal (August 2006)
- None of the widely touted new technologies and weapons systems "would have helped me in the last three years [in Iraq and Afghanistan]. But I could have used cultural training [and] language training. I could have used more products from American universities [who] understood the world does not revolve around America and [who] embrace coalitions and allies for all of the strengths that they bring us."
- Speaking at a professional conference on military transformation, urging the Pentagon to invest in efforts that would "diminish the conditions that drive people to sign up for these kinds of insurgencies." Breaking the Warrior Code (February 2005)
- In this age, I don’t care how tactically or operationally brilliant you are, if you cannot create harmony—even vicious harmony—on the battlefield based on trust across service lines, across coalition and national lines, and across civilian/military lines, you need to go home, because your leadership is obsolete. We have got to have officers who can create harmony across all those lines.
- At the May 2010 JFCOM Conference Ares blog, Aviation Week (June 2010)
- PowerPoint makes us stupid.
- Referring to the ubiquitous presentation software at a brief in North Carolina in April 2010, as quoted in We Have Met the Enemy and He Is PowerPoint (2010) by Elisabeth Bumiller, The New York Times
- Treachery has existed as long as there’s been warfare, and there’s always been a few people that you couldn’t trust.
- In response to a question during a congressional hearing about whether the U.S. should modify its Afghan strategy in response to six U.S. soldiers being killed by Afghan soldiers between Feb. 23 and March 1. As quoted in Key commanders have their say on Afghanistan (2012) by Walter Pincus, The Washington Post