diff --git a/day11/day11.jl b/day11/day11.jl
new file mode 100644
index 0000000..7d512e2
--- /dev/null
+++ b/day11/day11.jl
@@ -0,0 +1,99 @@
+#!/usr/bin/env julia
+
+using Test
+
+mutable struct Monkey
+  index :: UInt
+  items :: Vector{Int}
+  op :: Function
+  op_value :: Int
+  test_divisor :: Int
+  test_result :: NTuple{2, UInt}
+  inspected :: Int
+end
+
+function parse_monkey(text)
+  lines = split(text, '\n')
+  # Monkey 0:
+  match_index = match(r"Monkey (\d+):", lines[1])
+  index = parse(UInt, match_index.captures[1])
+  #   Starting items: 79, 98
+  match_items = match(r" *Starting items: (.*)", lines[2])
+  items_list = split(match_items.captures[1], ", ")
+  items = parse.(Int, items_list)
+  #   Operation: new = old * 19
+  match_op = match(r" *Operation: new = old (.) (old|\d+)", lines[3])
+  if match_op.captures[1] == "+"
+    op = +
+  elseif match_op.captures[1] == "*"
+    op = *
+  else
+    throw(DomainError("Unknown op: " * match_op.captures[1]))
+  end
+  if match_op.captures[2] == "old"
+    op = ^
+    op_value = 2
+  else
+    op_value = parse(Int, match_op.captures[2])
+  end
+  #   Test: divisible by 13
+  match_test = match(r" *Test: divisible by (\d+)", lines[4])
+  test_divisor = parse(Int, match_test.captures[1])
+  #   If true: throw to monkey 1
+  #   If false: throw to monkey 3
+  match_true = match(r" *If true: throw to monkey (\d+)", lines[5])
+  match_false = match(r" *If false: throw to monkey (\d+)", lines[6])
+  test_result = (parse(UInt, match_true.captures[1]) + 1,
+                 parse(UInt, match_false.captures[1]) + 1)
+  return Monkey(index, items, op, op_value, test_divisor, test_result, 0)
+end
+
+function read_monkeys(infile)
+  open(infile) do io
+    monkey_strings = split(read(io, String), "\n\n")
+    return parse_monkey.(monkey_strings)
+  end
+end
+
+function simian_shenanigans(monkeys :: Vector{Monkey})
+  for m in monkeys
+    for item in m.items
+      new_value = m.op(item, m.op_value)
+      new_value = Int(floor(new_value / 3))
+      new_monkey = (mod(new_value, m.test_divisor) == 0
+                    ? m.test_result[1] : m.test_result[2])
+      push!(monkeys[new_monkey].items, new_value)
+      m.inspected += 1
+    end
+    empty!(m.items)
+  end
+end
+
+function monkey_business(monkeys; rounds=20)
+  for _ in 1:rounds
+    simian_shenanigans(monkeys)
+  end
+  return prod(sort([m.inspected for m in monkeys])[end-1:end])
+end
+
+function test()
+  @testset "monkey business" verbose=true begin
+    @test monkey_business(read_monkeys("example.txt")) == 10605
+    @test monkey_business(read_monkeys("input.txt")) == 64032
+  end
+end
+
+function main()
+  if size(ARGS, 1) == 0
+    test()
+  else
+    infile = ARGS[1]
+    println("infile = ", infile)
+    monkeys = read_monkeys(infile)
+    display(monkeys)
+    println()
+    println("monkey business ", monkey_business(monkeys))
+  end
+end
+
+main()
diff --git a/day11/example.txt b/day11/example.txt
new file mode 100644
index 0000000..30e09e5
--- /dev/null
+++ b/day11/example.txt
@@ -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
diff --git a/day11/input.txt b/day11/input.txt
new file mode 100644
index 0000000..d5ddb7d
--- /dev/null
+++ b/day11/input.txt
@@ -0,0 +1,55 @@
+Monkey 0:
+  Starting items: 83, 88, 96, 79, 86, 88, 70
+  Operation: new = old * 5
+  Test: divisible by 11
+    If true: throw to monkey 2
+    If false: throw to monkey 3
+
+Monkey 1:
+  Starting items: 59, 63, 98, 85, 68, 72
+  Operation: new = old * 11
+  Test: divisible by 5
+    If true: throw to monkey 4
+    If false: throw to monkey 0
+
+Monkey 2:
+  Starting items: 90, 79, 97, 52, 90, 94, 71, 70
+  Operation: new = old + 2
+  Test: divisible by 19
+    If true: throw to monkey 5
+    If false: throw to monkey 6
+
+Monkey 3:
+  Starting items: 97, 55, 62
+  Operation: new = old + 5
+  Test: divisible by 13
+    If true: throw to monkey 2
+    If false: throw to monkey 6
+
+Monkey 4:
+  Starting items: 74, 54, 94, 76
+  Operation: new = old * old
+  Test: divisible by 7
+    If true: throw to monkey 0
+    If false: throw to monkey 3
+
+Monkey 5:
+  Starting items: 58
+  Operation: new = old + 4
+  Test: divisible by 17
+    If true: throw to monkey 7
+    If false: throw to monkey 1
+
+Monkey 6:
+  Starting items: 66, 63
+  Operation: new = old + 6
+  Test: divisible by 2
+    If true: throw to monkey 7
+    If false: throw to monkey 5
+
+Monkey 7:
+  Starting items: 56, 56, 90, 96, 68
+  Operation: new = old + 7
+  Test: divisible by 3
+    If true: throw to monkey 4
+    If false: throw to monkey 1