diff --git a/day11/day11.lisp b/day11/day11.lisp
new file mode 100644
index 0000000..3448010
--- /dev/null
+++ b/day11/day11.lisp
@@ -0,0 +1,93 @@
+(ql:quickload :cl-ppcre)
+
+(defclass monkey ()
+  ((items
+    :accessor items
+    :initarg :items
+    :type list)
+   (op
+    :accessor op
+    :initarg :op
+    :type function)
+   (test
+    :accessor test
+    :initarg :test
+    :type function)
+   (actions
+    :accessor actions
+    :initarg :actions
+    :type list)
+   (inspections
+    :accessor inspections
+    :initarg :inspections
+    :type number)))
+
+(defparameter *regexp* "Monkey (\\d+):\\n  Starting items: ([0-9, ]+)\\n  Operation: new = old ([\*\+]) (\\d+|\\w+)\\n  Test: divisible by (\\d+)\\n    If true: throw to monkey (\\d+)\\n    If false: throw to monkey (\\d+)")
+
+(defun str-to-list (str)
+  "Parses comma-separated string of integers in STR into a list of
+integers."
+  (loop :for item :in (ppcre:split ", " str) :collect (parse-integer item)))
+
+(defun make-op (operation operand)
+  "Returns a function matching the description given by STR."
+  (if (equal operand "old")
+      (if (equal operation "*")
+	  (lambda (old) (* old old))
+	  (lambda (old) (+ old old)))
+      (if (equal operation "*")
+	  (lambda (old) (* old (parse-integer operand)))
+	  (lambda (old) (+ old (parse-integer operand))))))
+
+(defun make-test (str)
+  "Returns a function testing for divisibility by the number given in
+STR."
+  (lambda (level) (zerop (mod level (parse-integer str)))))
+
+(defun throw-item (monkeys src dest)
+  "Removes the first item held by the monkey at position SRC in MONKEYS
+and adds it to the end of the items held by the monkey at position
+DEST in MONKEYS."
+  (progn
+    (setf (items (nth dest monkeys))
+	  (append (items (nth dest monkeys)) (list (car (items (nth src monkeys))))))
+    (setf (items (nth src monkeys))
+	  (cdr (items (nth src monkeys))))))
+
+(defun parse-input (input)
+  "Parses INPUT into a list of monkey objects."
+  (loop :for monkey
+	  :in (ppcre:split "\\n\\n" (uiop:read-file-string input))
+	:collect
+	(ppcre:do-register-groups (id items operation operand test true false) (*regexp* monkey)
+	  (return (make-instance 'monkey
+				 :items (str-to-list items)
+				 :op (make-op operation operand)
+				 :test (make-test test)
+				 :actions (list (parse-integer id) (parse-integer true)
+						(parse-integer id) (parse-integer false))
+				 :inspections 0)))))
+
+(defun run-round (monkeys div)
+  (let ((level 0))
+    (loop :for monkey :in monkeys :do
+      (loop :for item :in (items monkey) :do
+	(progn
+	  (setf (inspections monkey) (1+ (inspections monkey)))
+	  (setq level (funcall (op monkey) item))
+	  (setq level (floor level div))
+	  (setf (items monkey) (cons level (cdr (items monkey))))
+	  (if (funcall (test monkey) level)
+	      (throw-item monkeys (first (actions monkey)) (second (actions monkey)))
+	      (throw-item monkeys (third (actions monkey)) (fourth (actions monkey)))))))
+    monkeys))
+
+(defun solution (input div rounds)
+  "Run ROUNDS number of rounds on INPUT and use divisor DIV."
+  (let ((monkeys (parse-input input)))
+    (loop :for round :upto (1- rounds) :do
+      (run-round monkeys div))
+    (reduce '* (subseq (sort (loop :for monkey :in monkeys :collect (inspections monkey)) '>) 0 2))))
+
+(solution "./input" 3 20)
+(solution "./input" 1 10000)
diff --git a/day11/input b/day11/input
new file mode 100644
index 0000000..58fdc75
--- /dev/null
+++ b/day11/input
@@ -0,0 +1,55 @@
+Monkey 0:
+  Starting items: 91, 58, 52, 69, 95, 54
+  Operation: new = old * 13
+  Test: divisible by 7
+    If true: throw to monkey 1
+    If false: throw to monkey 5
+
+Monkey 1:
+  Starting items: 80, 80, 97, 84
+  Operation: new = old * old
+  Test: divisible by 3
+    If true: throw to monkey 3
+    If false: throw to monkey 5
+
+Monkey 2:
+  Starting items: 86, 92, 71
+  Operation: new = old + 7
+  Test: divisible by 2
+    If true: throw to monkey 0
+    If false: throw to monkey 4
+
+Monkey 3:
+  Starting items: 96, 90, 99, 76, 79, 85, 98, 61
+  Operation: new = old + 4
+  Test: divisible by 11
+    If true: throw to monkey 7
+    If false: throw to monkey 6
+
+Monkey 4:
+  Starting items: 60, 83, 68, 64, 73
+  Operation: new = old * 19
+  Test: divisible by 17
+    If true: throw to monkey 1
+    If false: throw to monkey 0
+
+Monkey 5:
+  Starting items: 96, 52, 52, 94, 76, 51, 57
+  Operation: new = old + 3
+  Test: divisible by 5
+    If true: throw to monkey 7
+    If false: throw to monkey 3
+
+Monkey 6:
+  Starting items: 75
+  Operation: new = old + 5
+  Test: divisible by 13
+    If true: throw to monkey 4
+    If false: throw to monkey 2
+
+Monkey 7:
+  Starting items: 83, 75
+  Operation: new = old + 1
+  Test: divisible by 19
+    If true: throw to monkey 2
+    If false: throw to monkey 6
diff --git a/day11/input-test b/day11/input-test
new file mode 100644
index 0000000..c04eddb
--- /dev/null
+++ b/day11/input-test
@@ -0,0 +1,27 @@
+Monkey 0:
+  Starting items: 79, 98
+  Operation: new = old * 19
+  Test: divisible by 23
+    If true: throw to monkey 2
+    If false: throw to monkey 3
+
+Monkey 1:
+  Starting items: 54, 65, 75, 74
+  Operation: new = old + 6
+  Test: divisible by 19
+    If true: throw to monkey 2
+    If false: throw to monkey 0
+
+Monkey 2:
+  Starting items: 79, 60, 97
+  Operation: new = old * old
+  Test: divisible by 13
+    If true: throw to monkey 1
+    If false: throw to monkey 3
+
+Monkey 3:
+  Starting items: 74
+  Operation: new = old + 3
+  Test: divisible by 17
+    If true: throw to monkey 0
+    If false: throw to monkey 1
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